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.
This+Electoral College
A third party is simply not viable without eliminating the Electoral College.
Unless...maybe you can keep it but you switch to a 2 round system and the two candidates with the most electors get to the 2nd round. But even then in practice i think it would be hard to convince people.
Poll
