But Trump hasn't based his tariff levies on the RTAA. Instead he cited the International Emergency Economic Powers Act (IEEPA). That justification was the basis of this Appeals Court ruling, and it's this assertion he'll have to defend before the Supreme Court.

Leaving aside the highly dubious nature of any claim that the existing trade imbalance constitutes a "national emergency" (a requirement of the IEEPA), there is the huge matter that the IEEPA makes precisely zero mention of tariffs. Moreover, Trump's tariffs were (correctly) stated by the court to be "unbounded in scope, amount and duration," while the IEEPA mandates narrowly-defined measures of specifically-stated fiscal amount and duration. To this layperson, this seems an absolutely no-brainer decision and the administration would have to re-state it's legal rationale (perhaps switching to whatever version of the RTAA remains in force at present, although if that were a viable legal strategy, it seems bizarre that it wouldn't have constituted the original claim, leaving the IEEPA argument as "Plan B."

But with this Supreme Court and it's unpredictable mix of partisan hacks and genuine jurists? It's a coin toss. That's no way to conduct political business in a functioning republic, but it is what it is in today's dysfunctional oligarchy.