The Supreme Court has recently signaled its interest in developing a new nondelegation test, one that would have courts more aggressively police Congress’s delegations of power to agencies. This could represent a death knell for significant climate action. The technical and scientific complexity of climate change mean that it is a problem uniquely suited to redress by expert agencies. If Congress is not permitted to delegate authority to agencies to address climate change, then it will be difficult for meaningful action against climate change to be taken at the federal level. With this threat in mind, this Article evaluates the emerging basis for the Court’s new nondelegation test: Chevron. The Court has hinted that it will look to two rules developed under Chevron to guide its revived nondelegation doctrine: the major questions doctrine and the jurisdictional exception that Chief Justice Roberts laid out in City of Arlington. By grounding the long-extinct nondelegation doctrine in the robust body of Chevron jurisprudence, the Court could give the nondelegation doctrine a legitimacy and specificity that a freeform version would lack. This Article argues, however, that transplanting the rules of Chevron to the nondelegation context would be doctrinally and logically incoherent. The Article first explains how the Court’s Chevron jurisprudence is based on a particular legal fiction about congressional delegation of authority to agencies. The Court has used this legal fiction to derive limiting principles for the application of Chevron deference, such as the major question doctrine and the City of Arlington jurisdictional exception. Importantly, Chevron’s limiting principles and the legal fiction underlying them are based on a principle of legislative supremacy, i.e., the understanding that Congress is supreme in the realm of policymaking, and thus courts’ role in interpreting statutes is to be agents of Congress. By contrast, the nondelegation doctrine as it is envisioned by the current Court relies on a notion of judicial supremacy: It imagines that courts have the final say as to what is acceptable policymaking, regardless of Congress’s intentions. Transferring Chevron to the nondelegation context would therefore amount to a categorical error. As a result, the Article concludes that, given the incompatible institutional framework underlying Chevron’s rules, the Court must look elsewhere for inspiration and support for its new nondelegation test.