This is my third offering on the most recent D.C. Circuit opinion in Guedes v. ATF, 920 F.3d 1 (D.C. Cir. 8/9/22), DCCir here, and GS here. My prior offerings are (chronological order): Important DC Circuit Opinion That Chevron Deference is Irrelevant if Agency Interpretation is Best Interpretation (Federal Tax Procedure Blog 8/9/22; 8/10/22), here; and § 7805(b) Time Limits Do Not Apply to Agency Best Interpretations of the Statute (Federal Tax Procedure Blog 8/11/22), here. (Note that I omitted from my original discussion the parallel Fifth Circuit opinion in Cargill v. Garland, 20 F.4th 1004 (5th Cir. 12/14/21), CA 5 here and GS here; see Fifth Circuit Affirms Agency Best Interpretation of Statute, thus Not Applying Chevron (Federal Tax Procedure Blog 12/20/21; 12/21/21), here.)
The point I want to make here explicit that which may be only implicit in my prior offerings. When courts defer (or parties (usually the Government) argue that a court should defer) to a “reasonable” agency interpretation, they often do not differentiate between (i) those reasonable agency interpretations that are the best interpretations and (ii) those agency interpretations that are not the best interpretations but are only reasonable agency interpretations qualifying for Chevron deference. Thus, by chanting "reasonable" and Chevron and appearing to defer, many (I think most) cases involve agency interpretations that are the best interpretations so there is no deference at all. That is the key point of this new Guedes opinion (and the Cargill opinion).
And,
that is why courts should, as did the court in the new Guedes and in Cargill opinions,
make clear what the best interpretation is so that they can either (i) apply
that interpretation without any nonsense about Chevron or (ii) apply Chevron
only when Chevron deference is outcome determinative – i.e., when the agency
interpretation is not the best interpretation. Keep in mind that, in making the determination as to the best interpretation, courts should give Skidmore respect (not deference) to the agency's interpretation because the agency, not the courts, has been assigned to administer the administrative scheme and is in a better position to deal with subtleties in administration than a court is. See Really, Skidmore "Deference?" (Federal Tax Procedure Blog 5/31/20; 2/14/21).
As to the latter applying Chevron deference only when the agency interpretation is not the best interpretation, I point readers to some discussion in my article John A. Townsend, The Report of the Death of the Interpretive Regulation Is an Exaggeration (SSRN December 14, 2021), https://ssrn.com/abstract=3400489:
In the postscript to the article (pp. 122-123) I offer the following reformulation of steps preserving Chevron's basic teaching but isolating when it is outcome determinative (footnotes omitted):