United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



                   Filed March 18, 2025

                       No. 23-1174

               CITY OF PORT ISABEL, ET AL.,
                       PETITIONERS

                             v.

       FEDERAL ENERGY REGULATORY COMMISSION,
                    RESPONDENT

RIO BRAVO PIPELINE COMPANY, LLC AND RIO GRANDE LNG,
                         LLC,
                     INTERVENORS




                Consolidated with 23-1221


              On Petitions for Panel Rehearing



    Nathan Matthews argued the cause for petitioners. With
him on the joint briefs were Lisa M. Diaz, Tom Gosselin, and
Gilberto Hinojosa. Eric E. Huber entered an appearance.
    Robert M. Kennedy, Senior Attorney, Federal Energy
Regulatory Commission, argued the cause for respondent.
With him on the brief were Matthew R. Christiansen, General
Counsel, and Robert H. Solomon, Solicitor. Jason Perkins,
Attorney, entered an appearance.

    Varu Chilakamarri argued the cause for intervenors Rio
Bravo Pipeline Company, LLC and Rio Grande LNG, LLC in
support of respondent. With her on the joint briefs were Jeremy
C. Marwell, Matthew X. Etchemendy, David L. Wochner, and
John Longstreth. James Dawson, Timothy J. Furdyna, James
D. Seegers, and Paul M. Teague entered appearances.
                       No. 23-1175

          CITY OF PORT ISABEL AND SIERRA CLUB,
                      PETITIONERS

                             v.

       FEDERAL ENERGY REGULATORY COMMISSION,
                    RESPONDENT

             TEXAS LNG BROWNSVILLE, LLC,
                     INTERVENOR




                Consolidated with 23-1222


              On Petitions for Panel Rehearing



    Nathan Matthews argued the cause for petitioners. With
him on the joint briefs were Lisa M. Diaz, Tom Gosselin, and
Gilberto Hinojosa.

    Robert M. Kennedy, Senior Attorney, Federal Energy
Regulatory Commission, argued the cause for respondent.
With him on the brief were Matthew R. Christiansen, General
Counsel, Robert H. Solomon, Solicitor, and Jason Perkins,
Attorney.
                               4

     Michael R. Pincus argued the cause for intervenor Texas
LNG Brownsville, LLC in support of respondent. With him on
the brief were Paul Korman and Mosby Perrow.

    Before: SRINIVASAN, Chief Judge, CHILDS and GARCIA,
Circuit Judges.

    Opinion for the Court filed by Circuit Judge GARCIA.

     GARCIA, Circuit Judge: In these cases, the court
considered petitions for review challenging the Federal Energy
Regulatory Commission’s reauthorization of two liquefied
natural gas terminals and an associated pipeline in Texas. See
City of Port Isabel v. FERC, 

 (D.C. Cir.
2024). In an opinion issued on August 6, 2024, we held that
the Commission had erred in four ways. Specifically, the
Commission failed to issue supplemental environmental
impact statements addressing its updated environmental justice
analysis, failed to treat a proposed carbon capture and
sequestration (CCS) system as a connected action, failed to
treat that system as a reasonable alternative, and failed to
adequately explain why it had declined to consider air quality
data from a nearby monitor. We further held that the
Commission’s decision to skip the first three procedures could
not be justified, and therefore required the Commission to
perform those procedures on remand. Based on those
procedural defects, the court vacated the reauthorization
orders.
     On October 21, 2024, the project applicants, as
respondent-intervenors, filed petitions for panel rehearing
disputing portions of the panel opinion’s merits analysis and
arguing that, at the least, any errors in the Commission’s orders
did not warrant vacatur. We directed the Commission and
petitioners to file responses.
                                   5
     Having considered the parties’ positions, the court
partially grants the petitions for rehearing to the extent that we
will remand without vacatur for the Commission to conduct
further proceedings. See, e.g., North Carolina v. EPA, 

, 1178 (D.C. Cir. 2008) (per curiam) (amending
opinion on rehearing in similar fashion); see also United States
Sugar Corp. v. EPA, 

 (D.C. Cir. 2016) (per
curiam); Nat’l Parks Conservation Ass’n v. Semonite, 

 (D.C. Cir. 2019) (per curiam). The parties also
dispute the impact of certain legal developments since the
panel opinion issued; as explained further below, we decline to
address those developments in the first instance, though we
acknowledge that they may alter the procedures the
Commission must conduct on remand.*
     In deciding whether to vacate agency action, this court
balances two factors: (1) “the seriousness of the order’s
deficiencies (and thus the extent of doubt whether the agency
chose correctly),” and (2) “the disruptive consequences” of
vacatur. Allied-Signal v. Nuclear Regul. Comm’n, 

, 150 (D.C. Cir. 1993) (quoting Int’l Union, UMW v.
FMSHA, 

, 967 (D.C. Cir. 1990)). In most cases,
the first factor asks whether the agency could “correct [the]
deficiencies” identified and reach the same ultimate decision.

     *
       Rio Grande LNG, LLC also informs us that, after the panel
opinion issued, it withdrew its proposal for a CCS system. Rio
Grande and Rio Bravo Pipeline Company, LLC now ask us to vacate
the connected action portion of the panel opinion as moot. The
original opinion acknowledged Rio Grande’s right not to proceed
with its CCS proposal, but Rio Grande’s unilateral choice to
withdraw the proposal does not warrant vacating the panel’s holding
on the subject. To the contrary, it is well established that a party may
not collaterally attack an opinion that we have already issued by
unilaterally mooting the controversy. See U.S. Bancorp Mortg. Co.
v. Bonner Mall P’ship, 

 (1994).
                               6
Oglala Sioux Tribe v. Nuclear Regul. Comm’n, 

 (D.C. Cir. 2018). In Standing Rock Sioux Tribe v. U.S.
Army Corps of Engineers, 

 (D.C. Cir. 2021),
however, we held that, “[w]hen an agency bypasses a
fundamental procedural step,” we assess the seriousness of an
order’s deficiencies by asking “not whether the ultimate action
could be justified, but whether the agency could, with further
explanation, justify its decision to skip that procedural step.”

.
     Standing Rock’s framing of the first Allied-Signal factor
ensures that agencies do not have an incentive to “build first
and conduct comprehensive reviews later.” 

 Under a
contrary rule, “[i]f an agency were reasonably confident that its
[environmental impact statement] would ultimately counsel in
favor of approval, there would be little reason to bear the
economic consequences of additional delay” by preparing the
statement before approving a project. 

 Standing Rock thus
teaches that the first Allied-Signal factor weighs in favor of
vacatur when there is no way for an agency to rehabilitate its
decision to skip a procedural step, even if the additional
procedure is unlikely to change the agency’s bottom line.
      Here, the panel applied Standing Rock’s reasoning to the
first Allied-Signal factor; rather than ask “only” whether the
Commission could likely reapprove the projects, the panel
asked whether the Commission could justify its decision to
omit the procedures it had skipped. 

 We said no, concluding
that on these specific facts, the Commission was required “to
issue a supplemental [environmental impact statement]” and to
consider the “CCS proposal . . . as either a connected action or
a project alternative.” Port Isabel, 

. We then
vacated the reauthorization orders because we found that the
“significant disruption vacatur may cause the projects” did not
“outweigh the seriousness of the Commission’s procedural
defects.” 

                               7
     That analysis appropriately relied on Standing Rock to the
extent it determined that the first Allied-Signal factor favored
vacatur because the Commission could not justify on remand
its choice to omit the procedures at issue. But it failed to
acknowledge that not all procedural omissions point toward
vacatur with the same force. Importantly, Standing Rock
concerned a truly “fundamental” procedural error: an agency’s
decision to authorize the construction of a pipeline without
issuing any environmental impact statement whatsoever. 

. We likened the error to that of “an agency that
bypassed required notice and comment rulemaking” altogether,
reasoning that completing a required environmental impact
statement went to the core of the agency’s responsibilities
under the National Environmental Policy Act (NEPA). 

     The procedural steps the Commission skipped here were
important, but they were not “fundamental” in the same sense.

 The Commission has already issued extensive final
environmental impact statements reflecting more than three
years of review and public comment. See No. 23-1174 J.A.
247–50; No. 23-1175 J.A. 201–03. Any further proceedings
the Commission would need to undertake pertain to specific,
discrete subjects; we are not confronted with a total and
unjustifiable failure to follow NEPA’s core procedures as to an
entire project, as we were in Standing Rock. Given all that the
Commission and the project applicants have done, we need not
be concerned that remand without vacatur in these
circumstances will create to the same degree an incentive to
“build first and conduct comprehensive reviews later.”
Standing Rock, 

.
    In sum, for the reasons Standing Rock gave, it is important
to the remedial analysis that the Commission’s procedural
choices were not merely inadequately explained, but
unjustifiable. Even so, we must account for the reality that the
procedures the Commission “bypasse[d]” were not quite
                               8
“fundamental.” 

 Properly considered, then, the first Allied-
Signal factor favors vacatur here, but not with nearly the force
that it did in Standing Rock or that our opinion ascribed to it.
     Against that backdrop, the seriousness of the
reauthorization orders’ deficiencies does not outweigh the
disruptive effects of vacatur. This court never doubted that
vacatur would impose significant disruptive consequences, see
Port Isabel, 

, and respondent-intervenors
have provided more details about those consequences in their
rehearing petitions, cf. Nat. Res. Def. Council v. EPA, 

 (D.C. Cir. 2006) (accounting for new information raised in
rehearing petition). These complex, large-scale projects have
been in development for over eight years. Vacatur would
upend the schedule for their construction, undermine
respondent-intervenors’ ability to meet binding contractual
commitments made in reliance on the Commission’s orders,
stall respondent-intervenors’ efforts to secure debt financing
and finalize labor contracts, and potentially prevent them from
supporting thousands of jobs in the local community.
Unnecessary delays in putting these projects into service could
have industry-wide effects; just one of the terminals is
projected to supply liquefied natural gas equal to
approximately 6% of current global demand when completed.
The Commission’s procedural missteps, though important, are
not so fundamental as to justify throwing the projects and those
reliant upon them into disarray.
    In submissions since the petitions for rehearing were filed,
the Commission and respondent-intervenors have offered
another reason why we might amend the panel opinion or
remand without vacatur: Two recent Executive Orders have
potentially altered the relevant legal landscape. When these
cases were briefed, argued, and decided, all parties took as
given that the Commission adhered to Executive Order 12,898,

 (Feb. 16, 1994), which required federal
                               9
agencies to identify and mitigate any disproportionate impacts
their activities may have on minority and low-income
populations. See, e.g., Order on Remand and Amending
Section 7 Certificate, Rio Grande LNG, LLC & Rio Bravo
Pipeline Co., 

, at P 103 (Apr. 21, 2023).
On January 21, 2025, President Trump revoked that Executive
Order. See Exec. Order No. 14,173 § 3(a)(i), 

, 8634 (Jan. 21, 2025). A second Executive Order
announced, among other things, that agencies may no longer
weigh any environmental considerations except those
expressly provided by statute. See Exec. Order No. 14,154 § 6,
90 Fed Reg. 8353, 8356 (Jan. 20, 2025). Respondent-
intervenors and the Commission argue, to varying degrees, that
these Executive Orders undermine the panel’s analysis of the
merits of these cases. See Rio Grande’s Fed. R. App. P. 28(j)
Letter at 1 (Jan. 23, 2025); Texas LNG Brownsville LLC’s Fed.
R. App. P. 28(j) Letter at 1–2 (Jan. 24, 2025); Commission’s
Response to Fed. R. App. P. 28(j) Letters at 1–2 (Feb. 6, 2025).
Petitioners, for their part, disagree. See Petitioners’ Response
to Fed. R. App. P. 28(j) Letters at 1–2 (Feb. 3, 2025).
     We decline to resolve these multi-faceted disputes over the
impact of the intervening Executive Orders in the first instance.
Doing so would not affect the court’s conclusion on rehearing
that vacatur is not warranted in these cases. Nor do these legal
developments alter the panel’s conclusion that, based on the
law and facts at the time of the Commission’s orders, and the
arguments timely presented to this court, the Commission’s
reasons for skipping the procedures at issue were arbitrary and
capricious and that the Commission would have been required
to conduct those procedures before deciding whether to
reauthorize the projects. Cf. Ctr. for Biological Diversity v.
FERC, 

, 1181 n.2 (D.C. Cir. 2023) (applying law
in effect at the time the Commission acted).
                              10
     These developments may, however, be highly relevant to
the Commission’s proceedings on remand. As respondent-
intervenors and the Commission suggest, the Executive Orders
give rise to new legal arguments that could justify a choice by
the Commission not to perform some or all of the procedural
steps that we held were required. Neither the initial panel
opinion nor this one prevents the Commission from attempting
to rehabilitate its chosen course on remand by drawing on legal
developments that were not before this court when the panel’s
initial decision issued. We leave it to the Commission to have
the “first word” on the Executive Orders’ implications for these
proceedings. Nat’l Fuel Gas Supply Corp. v. FERC, 

, 1249–50 (D.C. Cir. 1990) (per curiam) (noting “the
general principle that an agency should be afforded the first
word on how an intervening change in law affects an agency
decision pending review”).
    Accordingly, we remand these cases to the Commission
without vacating its orders.
                                                    So ordered.