The main thing you need is a much better constitution

Sure, but dictatorships don’t end without civil war

The US constitution kinda sucks and just trusts those in power to uphold democracy. Germany learned from Hitler that that isn’t the case, so their constitution provides multiple defences against a dictator that US lacks

Being intolerant of fascists does not make one a fascist. https://en.wikipedia.org/wiki/Paradox_of_tolerance

Not true, there have been multiple banned parties since WW2

This wouldn’t be a party banning another party, it would be the independent constitutional court