If you're going to make suppositions like that, of course, it would be just as feasible to examine this alternative scenario - In the original timeline, Hillary won. Enraged and invigorated by the GOP propaganda blitz against her, the GOP turns out in remarkable numbers and tricks a bunch of those who aren't paying attention as much to their side. Meanwhile, the Democrats grow a bit too complacent - they won, after all, and they don't really like that candidate anyways because of the GOP lies and her failure to get much done because of Republican sabotage, allowing the GOP to have a massive red wave. Emboldened by their success, the far right groups pushing for a Constitutional Convention get their desire, as well as permanent gerrymanders in a bunch of states and the US ends up in much the same condition as they've already given Chile. With the US then completely out of the game when it comes to addressing the Climate emergency, massive worldwide disaster becomes pretty much inevitable and happens.
Then comes the time traveler with a plan - get Trump to win and let the people actually see how horrendous the GOP actually is, leading to blue wave after blue wave, getting the US into the fight and keeping it there and producing some hope of preventing or significantly reducing the effects of the massive disaster to come.
Plenty more detail could be added, of course, but that would be just as feasible a scenario to work with.