One problem is that the Wiemar Republic had a trillion different parties, which further eroded their democratic institutions.

That's an argument for rank-based voting.

But it's also the only thing that prevented the Communists from coming to power, they were in majority. Hitler did everything he could to convert the Communists - that's what all the low-IQ marching and chanting was about.

Communists would have still won the 1933 election if SPD and KPD were to unite. They were all cut-throat Marxists, and their disagreement was minor. Don't believe the Bernietard propaganda about "social democracy" - Lenin, Trotsky, and Stalin called themselves "social democrats" too!

Social Democrats aside, do you think Trump supporters would've been for or against the Republic?

Maybe my right-libertarian background is showing. Do you want everything dictated from Berlin Washington DC, or to have more power in state and local governments?

In both cases (Germany since the unification, and gradually in the US), the Federal government had grabbed far too much power. Both needed a more decentralized Republic with a stricter constitution (like Switzerland).

Trump supporters are only "nationalist" in the sense that we don't want bad ideas from Europe (socialism) and we don't want Communist China to take over the world. The Demonrats are the real "nationalists": they want to do everything on the national level, and would use military force to crush any secession.

I’m for civic nationalism.

I am entirely against it. I have nothing in common with the Democrats. They are my enemy.

A party that also largely resented the Republic

Yes. That's the German version of "State's Rights".

Germany was originally several hundred principalities under a very loose confederacy. Some of those mostly-independent states (especially in the Protestant North) were the best educated, most industrious, and freest places in Europe. The First Reich was the Best Reich!

That system was destroyed by French aggression - remember Napoleon? Germany had to unify in order to compete (especially militarily) with the empires that surrounded it. That gave Prussia the excuse to take everything over by force and impose a strong central government. That was in 1871, still within living memory of the Weimar Republic...

Swiss cantons (along with the fully sovereign Liechtenstein) still somewhat resemble the old German idea that local governance is best.

only barely wound up resisting calls to merge with the NSDAP before it was disbanded?

Citation needed. It held off supporting the NSDAP until the NSDAP broke them by force.

And remember that at the time the NSDAP was responding to a crisis. The Commies and Communists were in majority (SPD+KPD), and a much bigger threat. Radical communists were carrying out a campaign of terrorism and assassination.