Justice Gorsuch's majority opinion in SAS Institute v. IANCU, 138 S. Ct. 1348, 1359 (2018), explained that "[e]ven under Chevron,we owe an agency's interpretation of the law no deference unless, after 'employing traditional tools of statutory construction,' we find ourselves unable to discern Congress's meaning." Read that again . . . slowly. If you take it seriously--i.e. if courts cannot proceed to step two unless they find themselves unable to discern Congress's meaning after squeezing every bit of juice out of the traditional tools of statutory construction possible--then Chevron is arguably dead letter.
In cases decided before Chevron (and in statutory interpretation cases that arise today but outside of Chevron's "domain,") courts are almost always able to find a way to say what the law is. With rare exceptions (like where a statute is void for vagueness), they never throw up their hands and declare themselves "unable to discern Congress's meaning." As a result, following IANCU's instructions should mean resolving virtually every Chevron case at step one. In other words, it should mean the end of Chevron.
And because Brand X teaches that questions of statutory interpretation that a court was able to resolve at step one must prevail over any subsequent conflicting agency interpretation, IANCU's aggressive approach to step one would effectively make it impossible for an agency to overrule any existing judicial interpretation.
Maybe the five-Justice majority in IANCU just got sloppy and described the standard more broadly than they actually intended. I doubt it, though. We are talking about Chief Justice Roberts and Justices Kennedy, Thomas, Alito, and Gorsuch, after all. Not exactly a group prone to sloppy word choice, particularly when describing the much-dissected Chevron standard in a case where the Court was asked to overrule its canonical two-step framework.
So, have I convinced you that IANCU effectively overruled Chevron and Brand X? What am I missing?