EDIT: On desktop, pasting in from the dissent:
(Kagan's words) Consider a few examples from the caselaw. They will help show what a typical Chevron question looks like—or really, what a typical Chevron question is. Because when choosing whether to send some class of questions mainly to a court, or mainly to an agency, abstract analysis can only go so far; indeed, it may obscure what matters most. So I begin with the concrete:
- Under the Public Health Service Act, the Food and Drug Administration (FDA) regulates “biological product[s],” including “protein[s].” 42 U. S. C. §262(i)(1). When does an alpha amino acid polymer qualify as such a “protein”? Must it have a specific, defined sequence of amino acids? See Teva Pharmaceuticals USA, Inc. v. FDA, 514 F. Supp. 3d 66, 79–80, 93–106 (DC 2020).
- Under the Endangered Species Act, the Fish and Wild- life Service must designate endangered “vertebrate fish or wildlife” species, including “distinct population seg- ment[s]” of those species. 16 U. S. C. §1532(16); see §1533. What makes one population segment “distinct” from another? Must the Service treat the Washington State population of western gray squirrels as “distinct” because it is geographically separated from other western gray squirrels? Or can the Service take into account that the genetic makeup of the Washington population does not differ markedly from the rest? See Northwest Ecosystem Alliance v. United States Fish and Wildlife Serv., 475 F. 3d 1136, 1140–1145, 1149 (CA9 2007).
- Under the Medicare program, reimbursements to hospitals are adjusted to reflect “differences in hospital wage levels” across “geographic area[s].” 42 U. S. C. §1395ww(d)(3)(E)(i). How should the Department of Health and Human Services measure a “geographic area”? By city? By county? By metropolitan area? See Bellevue Hospital Center v. Leavitt, 443 F. 3d 163, 174– 176 (CA2 2006).
- Congress directed the Department of the Interior and the Federal Aviation Administration to reduce noise from aircraft flying over Grand Canyon National Park—specifically, to “provide for substantial restoration of the natural quiet.” §3(b)(1), 101 Stat. 676; see §3(b)(2). How much noise is consistent with “the natural quiet”? And how much of the park, for how many hours a day, must be that quiet for the “substantial restoration” requirement to be met? See Grand Canyon Air Tour Coalition v. FAA, 154 F. 3d 455, 466–467, 474–475 (CADC 1998).