> My state does all elections by mail now. How would this even work?

Trump told Congress to ban most mail ballots.

> All this is on top of the fact that elections are run by the states, not the national government. Would such a law even be constitutional?

Experts said no. But this Supreme Court surprised experts before. And the constitution said Congress could decide elections of Congress. They have the power. They need an explanation enough people would accept.

It's not really up to Trump or Congress though is it?

Elections are run by the several states.