Will the 2 party duopoly ever end?

[Former President tack50]

Why would it in a first past the post system?

Well, the UK and Canada both use FPTP and have semi-relevant third parties but they are also parliamentary. Similarly France has a similar-ish political system to the US but with 2 rounds elections and has third parties

I think it is the combination of both 1 round presidential elections + FPTP that makes third parties completely non-existent.

If looking for a third party, honestly I think the most viable route would actually be to admit Puerto Rico as a state, given that the political system there is completely different than the rest of the US. Though it would be a third party in name only I suppose.

[Former President tack50]

If we had a Parliamentary system, there could be room for more than two parties, but while that works well in places like Germany, in Israel it has resulted in a party that gets 28% of the vote controlling the country's entire destiny. I could easily see a Trump rump of Republicans controlling everything by dividing and splintering everyone who opposed them. A 35% plurality would be forever in the driver's seat.

Uh, no it wouldn't? In Israel a party with 28% of the vote controls the country because the rest of parliament lets them do so.

But there are plenty of examples in parliamentary systems of a party with a large plurality not being in the driver's seat (let alone being there forever). New Zealand is a good example, since National got a huge plurality of 44.5% yet it was Labor who ended up ruling the country.

West Germany in the 1960s and 1970s also offers anothe example, where the CDU got pluralities in all elections except 1972; yet it was the SPD who ended up ruling the country.

If the "Trumpist party" ended up controlling the country with a 35% plurality forever it'd be because the rest of parliament lets them

Not to mention, if the US kept FPTP, the 2 party system, while weakened, would not go fully away. Just look at the UK.