Edit: please note that I made at least one mistake here (as well as some kind of boneheaded comments later). FPTP, even in the US, does not require a 50% majority, just more votes than anyone else (a "plurality"). It can still benefit parties to get to 50%, since it makes their winning more likely, and so in the absence of any drawbacks, most successful parties will still aim for it, but it isn't strictly necessary, as has been sometimes demonstrated in the UK. Thanks to squaresinger for linking a YouTube video that mentions this below. /Edit
I just want to share my thoughts on this. It started as a response to one comment, but I realized that there's a lot more that can (and I think should) be said, so here goes.
First, for those who don't know, FPTP stands for First Past The Post, meaning a system where everyone votes for a single candidate and whoever gets more than 50% (i.e. "past the post") wins the entire election (the losers get nothing). For many Americans, this might be so familiar that one would wonder how it could be any different (in a small-d democratic system), but there are in fact many alternatives: ranked voting, proportional representation, Condorcet method, etc.
They all have strengths and weaknesses, but for FPTP, and other similar systems, there's a result in political science called Duverger's law that says FPTP-like rules tend to cause a two-party system, essentially because because even if you don't team up with a larger party you may disagree with on many issues, to get a majority, others will, and then they'll win and you'll get nothing. And since getting significantly more than 50% consumes party resources that might better be used elsewhere, but gives no reward, 50% (plus a small "safety margin") is what all the successful parties will eventually aim for, and thus you get two roughly equally-successful parties. Tiny swings in voting then lead to massive differences in outcomes, which threatens the stability and security of everyone (even America's "enemies").
So saying "just vote for third parties" (like I see some calling for here) is tone-deaf at best, or part of a cynical ploy to fracture the opponent's party at worst. Even if a "third party" does win, the best that can be hoped for under FPTP is they just end up replacing one of the two parties, becoming one of the two parties in the "new" two-party system. And the two existing parties have likely spent far more time and effort researching ways to stop even that from happening than any of us ever will.
If we, as Americans, or others with a stake in what America decides to do, want to change this (and I personally do), then we need far more fundamental changes to how the system works. Just choosing a candidate we like (whether they have any chance of winning or not) won't cut it. I don't know what's the best voting system to use, but I know I'd like to scrap the Electoral College, for a couple reasons:
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Even though one might argue that Congress and the Supreme Court are more essential to reform, it's hard to deny that the President has a very large leadership role today.
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One might argue that relying on a convoluted/Byzantine method for choosing the President makes it harder to manipulate, and that's probably true, but the two parties have shown that it being difficult is not a deterrent to them doing so: in fact, they likely both benefit from it by keeping smaller parties that can't afford to do it out.
It reminds me of the fallacy in computer security of "security through obscurity": if it's possible to break into the system, and large numbers of people can benefit substantially from it, then someone eventually will, no matter how hard we make it to exploit. We need to change the system, not only so that it is prohibitively difficult for anyone to exploit the system, but also to get rid of a lot of the corruption that makes most people want to exploit it in the first place.
All of this is much easier said than done, I know, but we need to explain clearly to the public why "quick fixes" won't work, before we can convince them of the need for more fundamental changes. We still need to work on figuring out the details of the best changes, but unless we can show people the reality of the deep structural problems that acually exist, why they exist, and how we know we're right about what we're saying, we'll never convince most people to change anything.