Essentially, we do have more than two parties but the two major parties have a total stranglehold on the electoral process. Other parties run but they don't get a tiny fraction of the press or support that the two major parties get. They could not get on debate stages due to the rules allowing them to participate and they get a miniscule number of votes. The whole Electoral College deal is set-up just to favor Democrats and Republicans. So, you would need to abolish that and there is no way in hell Republicans would allow that because through the Electoral College they actually have a shot to win a presidential election because they control more states, but a smaller population, than Democrats do. So, through all the voter suppression stuff they do, gerrymandering, redistricting to a fair thee well, they can control the country with a much smaller number of voters. If we ran presidential elections off a popular vote the Republicans would never win again. Hence, they will say it is totally unfair to get rid of the Electoral College. 

With our elections being so frantically life or death now many people are voting just to try to stop a major candidate and not out of any understanding of what may happen to the country. So, voters are now mostly unwilling to support someone outside of Democrats or Republicans because it is like throwing your vote away and likely giving an advantage to a person or persons you don't want to see elected. 

Trump is not a Republican but to win an election he had to call himself one. If he ran as an independent, well, he likely would never have been elected. Trump does not care about parties but he needed to declare as a Republican to win an election. 

I think the only path to a viable third party is for one or both of the major parties to split. The issue is, neither party wants to do that because it weakens them drastically. If one party splits and the other does not, well, the party that stays together has a huge advantage. 

Republicans threatened to split but did not, because they know that would be a horror show for them. Plus right now if the Republicans split, it would be for one party to remain the Republicans and the other party to be the MAGA party with all the scum and lunatics. This would be interesting but highly unlikely. I think the sane Republicans think they can ride out the MAGA idiots and that once Trump is gone, people like Margorie Green and those clowns will lose traction. I think Bobert is on the verge of losing her reelection bid but it is close. Sad that anybody would vote for people like this but again, Republicans have done nearly nothing to prevent it. They won't speak up and get rid of their own garbage. 

So, I think the solution is the Republicans have to cut ties with the MAGA cult. Hard to do but if you are going to lose elections with them what does it matter if you lose some elections without them.