This assumes party identification and party goals are arbitrary.
That might be true in some cases (at least if “arbitrary” includes accidents of biography and consequent trust), but I suspect there are more supporters of both parties who actually identify with the explicit platform goals or projected values than there are people who are only against the other party.
I will go further here: the idea that there is a mass of people out there waiting to support a third party that would somehow better represent Americans is entirely without merit. How can you tell? Simple. Watch primaries. Any spoiler effect should be weak there. You can feel free to cast your ballot for whoever you like most without worrying that the candidate from the party you like the least will win without you supporting your second least.
But in spite of that freedom... we still see third party primary participation that’s multiple orders of magnitude down from primary participation focused on the big two.
I think the most straightforward explanation for this is that a vanishing fraction of Americans are ever likely to support more than two parties.
> This assumes party identification and party goals are arbitrary.
No, it just assumes (which is true) that people care about different aspects of the party platform. All over the developed world, people on both sides of the aisle want to reduce immigration. Left-leaning parties in Denmark and New Zealand (the beloved Jacinda Ardern) campaigned and won on platforms calling for reduced immigration. Mainstream center-left politicians like Macron have shifted to calling for increased integration.
In the U.S., that left has radicalized that debate. Democrats have dismissed all such concerns are racist. The moderate candidate Democrats ran didn't push back on any of that or acknowledge there was a legitimate debate to be had over immigration levels. And nearly everyone who ran in the Democratic primary embraced far-left positions such as decriminalizing illegal immigration and universal healthcare for undocumented immigrants--positions only 1-2 EU countries have embraced. (Due to a lack of any pushback on those positions from Biden, it was easier to get those primary positions to stick to him.) Biden wouldn't even take the completely mainstream Democratic position of condemning illegal immigration and calling for secure borders, which Obama embraced.
At that point, what do you do? A party isn't a single person or policy position; its an entire ideology (and the Democratic Party has become increasingly ideological).
You're underestimating the total number of people who just associate themselves with a party arbitrarily and vote down the party line IMO - but even ignoring that I disagree that people wouldn't vote for third parties if they were truly viable alternatives. A LOT of people in the Republican party in fact are repulsed by Trump; and there is also an obvious distinction in the Democratic party between AOC/Bernie-style progressive factions, and centrists and moderates in the party like what Biden represents. The super-crowded Democratic primaries made that pretty clear.
I think the big problem with the system as it stands is that people rightfully understand that if they vote for a third party candidate, that candidate is a) guaranteed to lose, b) guaranteed to be unable to enact any change in government without having a literal majority in the senate, and c) guaranteed to steal votes from a candidate who you may not love but is the lesser of two evils (plenty of libertarians do not agree with Biden much at all, but would rather have him than Trump/vice versa, and then vote down the party lines to avoid disaster).
Third party votes are often cast as a waste of a vote - and I don't blame people for thinking that way, because the system encourages it.
I will go further here: the idea that there is a mass of people out there waiting to support a third party that would somehow better represent Americans is entirely without merit
A huge number of Americans are socially conservative and economically liberal and there is currently no party that really supports that point of view.
That might be true in some cases (at least if “arbitrary” includes accidents of biography and consequent trust), but I suspect there are more supporters of both parties who actually identify with the explicit platform goals or projected values than there are people who are only against the other party.
I will go further here: the idea that there is a mass of people out there waiting to support a third party that would somehow better represent Americans is entirely without merit. How can you tell? Simple. Watch primaries. Any spoiler effect should be weak there. You can feel free to cast your ballot for whoever you like most without worrying that the candidate from the party you like the least will win without you supporting your second least.
But in spite of that freedom... we still see third party primary participation that’s multiple orders of magnitude down from primary participation focused on the big two.
I think the most straightforward explanation for this is that a vanishing fraction of Americans are ever likely to support more than two parties.