Dissenting opinion filed by Circuit Judge Tatel.
Millett, Circuit Judge *541A dispute between passenger and freight trains over priority access to railroad tracks has turned into a legal donnybrook over the bounds of congressional power. This court previously held that Congress went off the constitutional rails by empowering Amtrak to establish metrics and standards affecting track usage over the opposition of the private freight railroads that own those tracks and without the intermediation and control of a neutral governmental decisionmaker. More specifically, this court ruled that the Due Process Clause does not allow Amtrak to use an arbitration process to impose its preferred metrics and standards on its competitors, notwithstanding their opposition and that of the Federal Railroad Administration.
The question in this case is how to remedy that constitutional problem. We hold that severing the arbitration provision is the proper remedy. Without an arbitrator's stamp of approval, Amtrak cannot unilaterally impose its metrics and standards on objecting freight railroads. No rule will go into effect without the approval and permission of a neutral federal agency. That brings the process of formulating metrics and standards back into the constitutional fold.
I
A
The Rail Passenger Service Act of 1970, Pub. L. No. 91-518, 84 Stat. 1327, established Amtrak (a/k/a the National Passenger Railroad Corporation) to "reinvigorate a national passenger rail system that had * * * grown moribund and unprofitable," Association of American R.R. v. Department of Transp. , 721 F.3d 666, 668 (D.C. Cir. 2013) ( American Railroads I ), and "to fully develop the potential of modern rail service in meeting the Nation's intercity passenger transportation requirements," Rail Passenger Service Act § 301, 84 Stat. at 1330. In passing that legislation, "Congress recognized that Amtrak, of necessity, must rely for most of its operations on track systems owned by the [regional] freight railroads." Department of Transp. v. Association of American R.R. (American Railroads II) , --- U.S. ----, 135 S.Ct. 1225, 1229, 191 L.Ed.2d 153 (2015).
*542Three years later, Congress granted Amtrak's passenger rail service "preference over freight transportation in using a rail line[.]" 49 U.S.C. § 24308(c). To implement that priority system, Congress authorized Amtrak to enter into agreements with rail carriers and regional transportation authorities "to use [the] facilities of, and have services provided by, the carrier or authority under terms on which the parties agree." Id . § 24308(a). Congress added that the "terms shall include a penalty for untimely performance" by either party. Id . If Amtrak and the carrier or authority could not agree on governing terms, Congress empowered the federal Surface Transportation Board to "order that the facilities be made available and the services provided to Amtrak," and to "prescribe reasonable terms and compensation for using the facilities and providing the services." Id .1
In 2008, Congress enacted the Passenger Rail Investment and Improvement Act ("2008 Rail Act"), Pub. L. No. 110-432, 122 Stat. 4848,codified at 49 U.S.C. § 24101 note. That statute reconfigured the process for Amtrak to coordinate its rail access with private freight railroads. As is most relevant here, the Act directed that Amtrak and the Department of Transportation's Federal Railroad Administration "shall jointly * * * develop new or [shall] improve existing metrics and minimum standards for measuring the performance and service quality of intercity passenger train operations, including cost recovery, on-time performance and minutes of delay, ridership, on-board services, stations, facilities, equipment, and other services." Id. § 207(a). As part of that process, the 2008 Rail Act requires Amtrak and the Administration to "consult[ ] with" the Surface Transportation Board, rail carriers over whose rail lines Amtrak trains operate, States, passenger representatives, and Amtrak employees about the appropriate metrics and standards. Id .
If Amtrak and the Administration are unable to develop those metrics and standards within 180 days, Congress authorized "any party involved in the development of those standards" to "petition the Surface Transportation Board to appoint an arbitrator to assist the parties in resolving their disputes through binding arbitration." 2008 Rail Act § 207(d), 49 U.S.C. § 24101 note.
B
In tracing the history of this litigation, we write on a full slate. In March 2009, Amtrak and the Federal Railroad Administration published a Federal Register notice inviting comments on proposed metrics and standards pertaining to Amtrak's invocation of its right under the 2008 Rail Act to priority access to the railways. The Association of American Railroads ("Railroad Association") is a group of large freight railroad owners that operate tracks that Amtrak uses. The Railroad Association and its members submitted numerous comments, mostly concerning the increased expense associated with expanding and maintaining the needed track capacity and the timing metrics. See, e.g., J.A. 165, 171, 176.
The final metrics and standards that issued in May 2010 did not alleviate the Railroad Association's concerns. So the Railroad Association filed suit in federal district court challenging the facial constitutionality *543of Section 207's scheme for promulgating metrics and standards. The Railroad Association argued that the provision unconstitutionally delegated regulatory power over private entities to Amtrak, an allegedly non-governmental entity, by allowing it to influence or control the content of the metrics and standards imposed on its competitors. American Railroads Mot. for Summ. J., Association of American R.R. v. Department of Transp. , Civ. No. 11-1499 (D.D.C. May 31, 2012), ECF No. 8 at 7. The district court found no constitutional problem and granted summary judgment for the government. Association of American R.R. v. Department of Transp. , Civ. No. 11-1499 (D.D.C. May 31, 2012), ECF No. 17 at 2.
On appeal, this court deemed Amtrak to be a private entity and ruled that Section 207 unconstitutionally delegated authority to a private party "to jointly develop performance measures to enhance enforcement of the statutory priority Amtrak's passenger rail service has over other [private freight] trains." American Railroads I , 721 F.3d at 668.
The Supreme Court vacated that constitutional ruling. American Railroads II , 135 S.Ct. at 1234. The Court emphasized that "Amtrak was created by the Government, is controlled by the Government, and operates for the Government's benefit." Id. at 1232. Consequently, when undertaking "its joint issuance of the metrics and standards with the [Federal Railroad Administration], Amtrak acted as a governmental entity for the purposes of the Constitution's separation of powers provisions." Id . at 1232-1233. The Supreme Court then remanded the case for this court to address whether Section 207 ran afoul of the Fifth Amendment's Due Process Clause by giving Amtrak, a "for-profit corporation[,] regulatory authority over its own industry," and whether the arbitration provision violated the Appointments Clause, U.S. CONST., ART . II, § 2, CL. 2. American Railroads II , 135 S.Ct. at 1234.
On remand, this court again held Section 207 unconstitutional. Association of American R.R. v. Department of Transp. (American Railroads III) , 821 F.3d 19 (D.C. Cir. 2016). We held that Section 207 unconstitutionally delegated to Amtrak, a "self-interested entity," id . at 31, the authority to "regulate its resource competitors," id . at 23, in violation of the Due Process Clause.
This court rejected the government's argument that the Federal Railroad Administration's joint role in promulgating the metrics and standards tempered any due process concerns. We explained that the Administration "is powerless to overrule Amtrak" because, if there is "intractable disagreement between the two, the matter is resolved by an arbitrator, who may ultimately choose to side with Amtrak" in binding arbitration. American Railroads III , 821 F.3d at 35. Because the arbitration provision prevents the Administration from "keep[ing] Amtrak's naked self-interest in check," we concluded, "the requirement of joint development does not somehow sanitize the Act." Id . ; see id . at 34 n.4 (distinguishing Supreme Court precedent upholding joint regulatory efforts by "a self-interested group and a government agency" because the Administration's "authority to hold the line against overreaching by Amtrak is undermined by the power of the arbitrator" to independently authorize Amtrak's metrics and standards).
Lastly, this court held that appointment of the arbitrator violated the Constitution's Appointments Clause. This court concluded that the arbitrator's binding decision constituted final agency action. Yet the arbitrator was not appointed by the President, *544but rather by an independent agency, the Surface Transportation Board, which also had no oversight or review of the arbitrator's decision. American Railroads III , 821 F.3d at 38-39.
The case then returned to district court to remedy the constitutional violations. With the agreement of both the Railroad Association and the government, the district court vacated the May 2010 metrics and standards. Association of American R.R. v. Department of Transp. , Civ. No. 11-1499 (D.D.C. Mar. 23, 2017), ECF No. 27 at 6. The district court then declared Section 207's entire Amtrak-influenced process for formulating metrics and standards unconstitutional, rejecting the government's argument that severing Section 207(d)'s arbitration provision by itself would cure the identified constitutional infirmities. Id. at 5.
II
The district court had jurisdiction over this case under 28 U.S.C. § 1331, and we have jurisdiction to review its final order under 28 U.S.C. § 1291. We review de novo questions concerning the remediation of a statute's unconstitutionality and questions of statutory construction. See Stop This Insanity Inc. Employee Leadership Fund v. FEC , 761 F.3d 10, 13 (D.C. Cir. 2014).
Now at round four of this appellate litigation, we reach the question of how to remediate the constitutional violations previously found. The government does not challenge the prior panel's constitutional holdings on this appeal and, in any event, we are bound by them. The district court vacated the most immediate byproduct of the constitutional violations-the metrics and standards adopted in May 2010-and that aspect of the district court's decision is final and is also not challenged on appeal. The question instead is how to constitutionally right the statutory ship going forward. Because the linchpin for Amtrak's ability to unconstitutionally exercise regulatory authority over its competitors was the 2008 Rail Act's binding arbitration provision, severing Section 207(d) will fully cure the constitutional violations found in American Railroads III .
Declaring unconstitutional an Act of Congress, duly adopted by the Legislative Branch and signed into law by the Executive, is one of the gravest powers courts exercise. Longstanding principles of constitutional avoidance caution courts against exercising that power unless it is strictly necessary to resolve a case. See, e.g. , Ashwander v. Tennessee Valley Auth. , 297 U.S. 288, 347, 56 S.Ct. 466, 80 L.Ed. 688 (1936) (Brandeis, J., concurring); Syracuse Peace Council v. FCC , 867 F.2d 654, 657 (D.C. Cir. 1989). And even when a constitutional question must be joined, courts must choose the narrowest constitutional path to decision. Plaut v. Spendthrift Farm, Inc. , 514 U.S. 211, 217, 115 S.Ct. 1447, 131 L.Ed.2d 328 (1995).
When a statute has been held to be unconstitutional, an important corollary to those principles of constitutional avoidance is that the remedy should be no more severe than necessary to cure the disease. When possible, courts must preserve as much of a statute as is constitutionally possible, because "[t]he cardinal principle of statutory construction is to save and not to destroy." Tilton v. Richardson , 403 U.S. 672, 684, 91 S.Ct. 2091, 29 L.Ed.2d 790 (1971) (quoting NLRB v. Jones & Laughlin Steel Corp. , 301 U.S. 1, 30, 57 S.Ct. 615, 81 L.Ed. 893 (1937) ).
Our decision in American Railroads III points us down that same narrow path. In *545concluding that the 2008 Rail Act's process for developing metrics and standards was unconstitutional, this court's analysis comprised two distinct determinations: (1) that Amtrak was economically self-interested in and competing with the freight railroads as to the content of the metrics and standards, and (2) the 2008 Rail Act endowed Amtrak with the power to regulate those competitors. American Railroads III , 821 F.3d at 31. Both prongs were required to make out a Due Process Clause violation. Id . at 31.
This court's resolution of that second prong identifies the arbitration provision as the critical constitutional fissure. After all, the constitutional problem in this case was not that Amtrak exercised some role in formulating those metrics and standards-Amtrak had some role under the 1970 Act and the 1973 amendment, which the freight railroads have not challenged. Plus Amtrak's participation to some extent is inherent in the development of contracts between Amtrak and individual freight railroads that embody those metrics and standards. See 49 U.S.C. § 24308(a).
Nor, as our prior opinion explained, would the Constitution prohibit Amtrak from exercising some measure of joint control with a disinterested governmental agency, as long as that agency's duty to protect the "public good" could check Amtrak's self-interest and prevent unfair harm to its competitors. American Railroads III , 821 F.3d at 29. Indeed, our prior opinion specifically noted that a number of arrangements by which regulatory measures were imposed through the "joint action of a self-interested group and a government agency" had passed constitutional muster. Id . at 34 n.4 (citing Currin v. Wallace , 306 U.S. 1, 59 S.Ct. 379, 83 L.Ed. 441 (1939) ; Sunshine Anthracite Coal Co. v. Adkins , 310 U.S. 381, 60 S.Ct. 907, 84 L.Ed. 1263 (1940) ).
Instead, the straw that broke the camel's back was that the 2008 Rail Act stripped the Federal Railroad Administration of that independent ability to temper or prevent Amtrak from adopting measures that promoted its own self-interest at the expense of its freight railroad competitors. It was Section 207(d)'s binding-arbitration provision that both gave Amtrak that independent regulatory muscle and disarmed the Administration. The 2008 Rail Act charged Amtrak and the Administration, at the outset, with developing the metrics and standards jointly. 2008 Rail Act § 207(a), 49 U.S.C. § 24101 note. But critically, if that collaborative process stalled, Section 207(d) allowed Amtrak on its own to request the appointment of a Surface Transportation Board arbitrator. 2008 Rail Act § 207(d), 49 U.S.C. § 24101 note. The arbitrator then had the authority, through binding arbitration, to force the promulgation of final metrics and standards regardless of the Administration's, the private freight railroads', or anyone else's objections to their terms. American Railroads III , 821 F.3d at 39.
So the arbitration provision is what constitutionally derailed the statutory scheme. For it empowered Amtrak to impose on its competitors rules formulated with its own self-interest in mind, without the controlling intermediation of a neutral federal agency. All Amtrak had to do was persuade the arbitrator to rule in its favor. Once that happened, the disinterested governmental agency-the Administration-"[wa]s powerless to overrule Amtrak." American Railroads III , 821 F.3d at 35. Whatever "equal authority" the Administration initially had with Amtrak by virtue of the charge to jointly develop the metrics and standards, that power would evaporate "[w]hen there is intractable disagreement between the two[.]" Id . At that point, "the matter is resolved by an arbitrator, who may ultimately choose to side with Amtrak."
*546Id . The Administration "cannot keep Amtrak's naked self-interest in check, and therefore the requirement of joint development does not somehow sanitize the [2008 Rail] Act." Id .
Emphasizing the centrality of the arbitration provision to our constitutional decision, this court pointed to Amtrak's arbitration escape hatch to distinguish Supreme Court precedent otherwise upholding programs for the joint private and governmental promulgation of regulations. For example, in Currin v. Wallace , the Tobacco Inspection Act of 1935, 7 U.S.C. §§ 511 et seq. , delegated to the Secretary of Agriculture the authority to set standards for various classes of tobacco that would affect the commodity's market pricing. 306 U.S. at 5-6, 59 S.Ct. 379. But the Secretary's proposed standards and prices would govern only if two-thirds of the tobacco growers within the market region approved them by referendum. Id. at 15, 59 S.Ct. 379. The Supreme Court upheld that provision because the Secretary's ultimate control over the content of the standards and prices submitted for approval meant that self-interested producers had neither the power to craft the rules in their own image nor to "force [them] upon a minority" of competitors. Id . ; see United States v. Rock Royal Co-operative, Inc. , 307 U.S. 533, 577-578, 59 S.Ct. 993, 83 L.Ed. 1446 (1939) (upholding marketing orders for milk because, even though they were approved by two-thirds of milk producers, the Secretary of Agriculture exercised ultimate control over the prices set).
Similarly, in Sunshine Anthracite Coal Co. v. Adkins , 310 U.S. 381, 60 S.Ct. 907, 84 L.Ed. 1263 (1940), the Supreme Court upheld a provision in the 1937 Bituminous Coal Act, 15 U.S.C. §§ 828 et seq. , under which participating coal producers could propose minimum coal prices to a government agency-the National Bituminous Coal Commission. The Coal Commission, however, retained complete authority to "approve[ ], disapprove[ ], or modif[y]" the prices ultimately adopted. Id . at 388, 60 S.Ct. 907 ; see id . at 399, 60 S.Ct. 907. Because the Commission exercised "authority and surveillance" over the participating coal producers, and because law-making remained in the hands of the agency and was "not entrusted to the industry," the Supreme Court declared the statutory scheme to be "unquestionably valid." Id . at 399, 60 S.Ct. 907.
The arbitration provision in the 2008 Rail Act broke from that mold. Ultimate control over the regulatory standards did not rest with a neutral governmental agency; it could be exercised by Amtrak with an assist from the arbitrator. American Railroads III , 821 F.3d at 34 n.4. "[T]he [Federal Railroad Administration's] authority to hold the line against overreaching by Amtrak," we explained, "is undermined by the power of the arbitrator." Id.
Said another way, without the ability to resort to binding arbitration, Amtrak would have no power to impose its own self-interested regulatory measures on its competitors. While Amtrak could press its views with the Federal Railroad Administration, unless the Administration independently determined that those standards were in the public interest-not just Amtrak's interests-Amtrak's proposals would hit a dead-end. See American Railroads I , 721 F.3d at 674 (stating that, if the regulatory authority to set metrics and standards is wielded by a governmental agency, "[Section] 207 is of no constitutional moment").
Our dissenting colleague reads our prior decision differently, concluding that *547American Railroads III constitutionally quarantined Amtrak away from any "participation" in the regulatory process "at all ," Dissent Op. at 551, 554, and forbade even efforts to "convinc[e]" or "persuade" the Federal Railroad Administration what the metrics and standards governing its own performance should be, id . at 554, 557.
But our prior opinion never said that the Constitution required sidelining Amtrak throughout the regulatory process. We were quite explicit about what the constitutional Due Process problem was: Notwithstanding its self-interest, the 2008 Rail Act empowered Amtrak "to regulate" its competitors and "to make law." 821 F.3d at 23 ; see id . at 27 ("Our view of the case can be reduced to a neat syllogism," which turns at each line of the syllogism on whether the Act gives Amtrak "regulatory authority"); id . (due process question turns on whether Amtrak has "rulemaking authority"); see also American Railroads II , 135 S.Ct. at 1234 (remanding for decision as to whether Amtrak unconstitutionally exercised "regulatory authority" over its competitors).
So the critical constitutional question is what in the 2008 Rail Act made Amtrak itself a regulator -that is, what allowed it to make law. It was not, we said, Amtrak's ability to engage in "joint [regulatory] action" with the Administration. Such joint efforts between "a self-interested group and a government agency," we specifically noted, raised no constitutional eyebrow as long as the government agency could "hold the line" against the entity's "overreaching" to advance its own self-interests. 821 F.3d at 34 n.4. The opinion then went on to explain that the critical check on private interests that had been present in those Supreme Court cases was missing here precisely because the "[Administration] is powerless to overrule Amtrak," and when there is "intractable disagreement between the two, the matter is resolved by an arbitrator, who may ultimately side with Amtrak." Id . at 35. As a result, the Administration "cannot keep Amtrak's naked self-interest in check." Id .
The dissenting opinion rightly notes our holding that the metrics and standards the Administration and Amtrak jointly develop are forms of regulation, 821 F.3d at 33-34, and reads our opinion as holding that the constitutional flaw was in vesting " 'Amtrak [with] the authority to develop [those] metrics and standards-constrained very partially ... by the [Administration] and the arbitrator[.]' " Dissent Op. at 555 (quoting 821 F.3d at 33 ). To the dissenting opinion, the ensuing discussion about joint rulemaking efforts and the Administration's and arbitrator's inability to rein Amtrak in was simply an explanatory aside just answering the government's argument about precedent. Dissent Op. at 556-57.
Our opinion said otherwise, explicitly wrapping the two points together. The source of the constitutional trouble, we explained, was that the 2008 Rail Act vested "Amtrak [with] the authority to develop [those] metrics and standards-constrained very partially, as discussed below , by the [Administration] and the arbitrator[.]" Id . at 33 (bold added). The referenced "discuss[ion] below" was precisely the analysis on the following pages of how the arbitration option allowed Amtrak to escape the type of check on its self-interest that the Due Process Clause requires when regulations are jointly developed between a government agency and self-interested groups. The two portions of the opinion cannot be delinked.
The crux of the constitutional problem, in short, was not that Amtrak had input or the opportunity to "persuade" the Administration. Dissent Op. at 557. That happens all the time in the regulatory process by *548all manner of self-interested parties. "[P]articipation" is not regulation. Id . at 551. What went wrong in the 2008 Rail Act was that Amtrak, through unilateral resort to the arbitrator, had the power "to make law," 821 F.3d at 23, by formulating regulatory metrics and standards without the agreement or control of the Administration.2
The dissenting opinion also objects that the Federal Railroad Administration itself is neither "disinterested" nor tasked with promoting the freight operators' interests. Dissent Op. at 557. Our prior decision never suggested that the Administration does not act in good faith to protect the public interest, just like the other agencies involved in joint regulatory development with private interests. To the contrary, it explicitly noted that if Congress had "directed the [Federal Railroad Administration] to develop [the metrics and standards] alone," Congress would have been giving regulatory power to a "presumptively disinterested" government entity. American Railroads III , 821 F.3d at 35 (quoting Carter Coal , 298 U.S. at 311, 56 S.Ct. 855 ). Anyhow, the relevant constitutional question, as our prior opinion explained, is whether the Administration can "check" Amtrak's self-interests, 821 F.3d at 35, not whether it can speak for a different self-interested group. With the arbitrator provision removed, the Administration can stop a self-serving Amtrak proposal dead in its tracks.
Finally, the dissenting opinion notes that the Administration is housed "in the same branch" of an Executive agency as Amtrak. Dissent Op. at 557. But that is just a reminder that, when it comes to formulating these metrics and standards, the Supreme Court has held that "Amtrak act[s] as a governmental entity," 135 S.Ct. at 1233, and thus is not purely animated by self-interest. That Amtrak has "public objectives" to serve, id . at 1232, is yet another reason that the constitutional remedy does not require completely walling Amtrak off from any role at all in the regulatory process.
* * * * *
Given all of that, eliminating the arbitration provision is the key to curing the constitutional problem because it eliminates Amtrak's ability and power to exercise regulatory authority over its competitors. Without the Administration's approval, Amtrak's regulatory proposals would amount to nothing more than trying to clap with one hand. Such an ineffective endeavor would not offend the Due Process Clause.
As a matter of constitutional law, excising Section 207(d)'s binding-arbitration provision would deprive Amtrak of its unlawful ability to engage in regulatory self-help. But a court may order such curative severance only if, as a matter of statutory construction, doing so would leave a functioning statutory scheme and would comport with congressional objectives. See United States v. Booker ¸ 543 U.S. 220, 258-259, 125 S.Ct. 738, 160 L.Ed.2d 621 (quotations omitted); see also Bismullah v. Gates , 551 F.3d 1068, 1071 (D.C. Cir. 2009) ("[W]e must retain those portions of the Act that are (1) constitutionally valid, (2) capable of functioning independently, and *549(3) consistent with Congress' basic objectives in enacting the statute.") (quotations omitted).
We hold that severing Section 207(d) is the proper medicine in this case, for four reasons.
First , there is a presumption in favor of severability. See , e.g. , United States v. National Treasury Employees Union , 513 U.S. 454, 488, 115 S.Ct. 1003, 130 L.Ed.2d 964 (1995) ; Bismullah , 551 F.3d at 1071 ; Alaska Airlines, Inc. v. Donovan , 766 F.2d 1550, 1560 (D.C. Cir. 1985). The "normal rule is that partial, rather than facial, invalidation is the required course." Free Enterprise Fund v. Public Co. Accounting Oversight Bd. , 561 U.S. 477, 508, 130 S.Ct. 3138, 177 L.Ed.2d 706 (2010) (internal quotation marks omitted).
That presumption enforces judicial restraint in constitutional adjudication by ensuring that, to the extent possible, courts "limit the solution to the problem, severing any problematic portions while leaving the remainder intact." Free Enterprise Fund , 561 U.S. at 508, 130 S.Ct. 3138 (internal quotation marks omitted). After all, "the unconstitutionality of a part of an Act" says nothing about "the validity of its remaining provisions[.]" Id . (internal quotation marks omitted).
To be sure, this question of statutory (re)construction would be easier if the 2008 Rail Act contained a severability clause. But it does not. Still, sometimes such congressional "silence is just that-silence[.]" New York v. United States , 505 U.S. 144, 186, 112 S.Ct. 2408, 120 L.Ed.2d 120 (1992) (internal quotation marks omitted). The absence of a severability clause cuts neither against nor in favor of severance; the presumption of severability remains intact. Id . ; see City of New Haven v. United States , 809 F.2d 900, 905 n.15 (D.C. Cir. 1987).
Second , as to the requirement that the statute be functional in the absence of the severed provision, the parallels between the trimmed down 2008 Rail Act and the original 1970 and 1973 schemes offer substantial assurance that the statutory scheme could function even with Section 207(d) pruned away. To be sure, negotiations over what metrics and standards to adopt may be harder without the binding-arbitration tiebreaker. But the Federal Railroad Administration and Amtrak have been working together on such matters for almost half a century, and most of that time without the possibility of resort to binding arbitration. We also assume that the Federal Railroad Administration and Amtrak, which wears a governmental hat in this role, American Railroads II , 135 S.Ct. at 1233, will endeavor to promulgate the required rules in good faith and consistently with their legislatively assigned duties, see CTIA-The Wireless Ass'n v. FCC , 530 F.3d 984, 989 (D.C. Cir. 2008) (agencies are presumed to exercise their duties in good faith).
Third , narrowly severing Section 207(d) would better comport with Congress's objectives than would throwing the entire Section 207 baby out with the bath water. In this regard, we do not inquire what Congress intended, since it undoubtedly intended the legislation as enacted. "The relevant question * * * is not whether the legislature would prefer (A+B) to B, because by reason of the invalidation of A that choice is no longer available." Leavitt v. Jane L. , 518 U.S. 137, 143, 116 S.Ct. 2068, 135 L.Ed.2d 443 (1996). Instead, we ask the more practical question of "whether the legislature would prefer not to have B if it could not have A as well." Id .
Severing Section 207(d) leaves intact Congress's objective of streamlining the process for formulating metrics and standards, and even strengthens the statutory *550command that the Federal Railroad Administration and Amtrak work "jointly" to develop those standards, 2008 Rail Act § 207(a), 49 U.S.C. § 24101 note, by eliminating Amtrak's unilateral ability to break away from that collaborative process. And by preserving the duty to consult with other interested parties, including the freight railroads, severance of the arbitration provision would continue the process of obtaining broad input on the standards.
In addition, nothing in the statutory text, structure, or legislative history indicates that Section 207 was meant to be an all-or-nothing provision or, more to the point, that the binding-arbitration provision was a legislative deal-breaker. Cf. Brockett v. Spokane Arcades, Inc. , 472 U.S. 491, 506, 105 S.Ct. 2794, 86 L.Ed.2d 394 (1985) (holding that severance is impermissible where there is evidence that the legislature "would not have passed it had it known the challenged provision was invalid").
Fourth , the Railroad Association argues that the government waived its ability to argue for severance by waiting until we remanded to the district court to first propose severance of Section 207(d). That argument fails. To begin with, the question of severance arises only after a statute has been held unconstitutional. It is thus unsurprising that the government devoted its efforts to vigorously defending the constitutionality of the 2008 Rail Act, and did not broach the severability question until the remedial stage of this litigation. The cases on which the Railroad Association relies fall wide of the mark since they involve instances in which the question of severability was not raised at all in the appellate briefing.3
In any event, severability is a doctrine borne out of constitutional-avoidance principles, respect for the separation of powers, and judicial circumspection when confronting legislation duly enacted by the co-equal branches of government. Parties cannot, by litigation tactics or oversight, compel the courts to strike down more of a law than the Constitution or statutory construction principles demand.
For all of those reasons, we hold that the proper constitutional remedy in this case is to sever Section 207(d)'s binding-arbitration provision and leave the balance of Section 207 and the 2008 Rail Act intact.
C
When the Supreme Court remanded this case, it left open for this court's consideration a separate constitutional question: whether the appointment of Amtrak's president by its Board and not the President violates the Appointments Clause, given that Amtrak's president had a vote in establishing the metrics and standards. American Railroads II, 135 S.Ct. at 1234 ; see 2008 Rail Act § 202(a), Pub. L. No. 110-432, 122 Stat. at 4911. In American Railroads III , this court found it unnecessary to resolve that question given the separate determination that the statutory scheme stepped over the Due Process Clause line. 821 F.3d at 23.
*551The Railroad Association has raised the issue again in this appeal. We cannot answer that question because it is now moot. See Iron Arrow Honor Society v. Heckler , 464 U.S. 67, 70, 104 S.Ct. 373, 78 L.Ed.2d 58 (1983). The May 2010 metrics and standards in which Amtrak's president had a role have already been vacated by the district court, and that unappealed aspect of the district court's decision is final. Nor does the Railroad Association face any forward-going risk of such an allegedly unconstitutional intrusion into the rulemaking process because Congress amended the statute in 2015 to require that the voting members of Amtrak's Board be appointed by the President and confirmed by the Senate. 49 U.S.C. § 24302(a)(1). As a result, the Railroad Association's Appointments Clause claim is moot, and we lack jurisdiction to address it.
We at long last come to the end of the tracks in this lengthy litigation. We hold that the constitutional violations previously identified by this court can be fully remedied by excising the binding-arbitration provision in Section 207(d) of the 2008 Rail Act, and that Section 207(d) is properly severable. The Railroad Association's Appointments Clause challenge is moot. We accordingly reverse the judgment of the district court and remand for the entry of judgment consistent with this opinion.
So ordered.