Document ID: ./input/supremecourt_opinions/opinions/23pdf/23a349_0813.pdf
Page Number: 16

Cite as:  603 U. S. ____ (2024) 

13 

Opinion of the Court 

command  the  same  emissions-control  measures  if  con-
ducted for, say, just one State.  Tr. of Oral Arg. 58–59.  Per-
haps there is some explanation why the number and iden-
tity  of participating States  does  not  affect  what measures 
maximize  cost-effective  downwind  air-quality  improve-
ments.  But if there is an explanation, it does not appear in 
the final rule.  As a result, the applicants are likely to pre-
vail on their argument that EPA’s final rule was not “rea-
sonably explained,” Prometheus Radio Project, 592 U. S., at 
423, that the agency failed to supply “a satisfactory expla-
nation  for  its  action[,]”  State  Farm  Mut.  Automobile  Ins. 
Co.,  463  U. S.,  at  43,  and  that  it  instead  ignored  “an  im-
portant  aspect  of  the  problem”  before  it,  ibid.    The  appli-
cants are therefore likely to be entitled to “revers[al]” of the 
FIP’s mandates on them.  §7607(d)(9).10 

III 
A 
  Resisting  this  conclusion,  EPA  advances  three  alterna-
tive arguments. 
  First, the government insists, the agency did offer a rea-
soned response to the applicants’ concern, just not the one 
they hoped.  When finalizing its rule in response to public 
comments, the government represents, “the agency did con-
sider whether the [FIP] could cogently be applied to a sub-
set  of  the  23  covered  States.”    EPA  Response  27;  see  also 
post, at 17–18 (BARRETT, J., dissenting).  And that consid-
eration, the government stresses, led EPA to add a “sever-
ability” provision to its final rule in which the agency an-
nounced that the FIP would “ ‘continue to be implemented’ ” 
without regard to the number of States remaining, even if 
just one State remained subject to its terms.  EPA Response 

—————— 

10 Various applicants offer various other reasons why they believe they 
are likely to succeed in challenging EPA’s FIP.  Having found that they 
are likely to succeed on the basis discussed above, however, we have no 
occasion to address those other arguments.