While the fears are real, the dangers are a different story. I'm assuming that you're a centrist Matthew. The republican party is objectively worse than the Democratic party. Many leftists have been disillusioned by the Dems and their status quo tendencies.
Neither party is worse, because the parties are an illusion. The left and right are barely represented by their respective parties. I've heard right populist and leftist opinions and there are three main agreements:
The Rich have too much power/money
They might have different names for it, but they hate fascismo (slightly different than facism.)
My party isn't listening
I know number two is gonna require some explanation. I'm describing it as Fascismo because its authoritarianism through goverment interaction and acquisition of businesses. Some also call this corporatism.
But the left and right call this capitalism and communism respectively. The reality is it's neither. This is closer to italian fascism. Hence the Italian word for Fascism, Fascismo.
And this is the main issue. The leftists and populist right have the same enemy. But the parties get them arguing over terminology and technicalities instead of defeating the common enemy. If they started campaigning against incumbents in a bipartisan manner we could get back to having the actual disagreements I've heard from leftists and the populist right.
The parties are distracting the people with word games and bullstuff while people suffer.
To many this sounds like I'm sucking off the Dems, but voting for the lesser of two evils is necessary for a leftist if they actually hope to change things. Giving any extra power to republicans is only going to damage the chances of changing the system. While corporate democrats aren't good either, they are much more easy to fight against than the mental borderline fascist republicans.
Corporate Democrats and Fascist Republicans are the same thing. They've just hooked you. Lesser of two evils voting is a trap.
If the democrats gain supermajority, then the only steps left are to gain enough power within the party and then change the election system to make it more amicable to 3rd parties.
Why would they do that? If either party gets a super majority the first thing they'll do is solidify their position in government.