Like every other kind of political legitimacy, judicial legitimacy is earned (or not)
It is extremely important to remember that the doctrine of judicial supremacy is something invented by the federal courts themselves. It is neither explicit or implicit in the Constitution itself, so this isn’t ONLY a matter of how many divisions does the Supreme Court et. al. have. It is also a matter of a purely pragmatic arrangement, that has been (mostly) tolerated by the rest of the federal government because it was convenient to do so for various reasons.
If the federal courts are taken over by the minions of an authoritarian national party, and used by that party to fundamentally undermine both liberal democracy and basic norms of bureaucratic legality — called more pompously “the rule of law” in American legal ideology — then those courts have forfeited their right to continue to enjoy that pragmatic accomodation.
We are very near to that point if we haven’t reached it already. It’s time for supporters of liberal democracy and legal regularity to fire some metaphorical shots across the bow of the federal courts, and if that doesn’t work, to take more drastic action.
Otherwise, those courts are simply going to make the electoral process completely irrelevant.