250k votes cast for Johnson and Stein in FL. If those broke for Hillary, she'd win.
Except you can't just assume 100% of those voters would have broken for Hillary. Libertarians aren't going to vote for Big Government Clinton, Bernie or Busters probably would have just stayed home if they hadn't had Jill Stein to vote for, and at least some Greens and Libertarians prob would have been accelerationists who thought America "deserved" Trump or some shit.
Third party candidates get votes in every election. If you didn't win without the third party voters, you didn't win, and blaming a group for doing what they ALWAYS do is just silly.
Rural whites turning the fuck up is the cause of this, plain and simple, and I'd say the phenomenally quick and sharp rise of stridently radical Leftist views on race, gender, sex, and other such things in the last four years is probably at the root of that. When you back people into a corner, they fight back, and history shows this again and again. Biden probably would have overcome this by virtue of being a million times more likable than Trump, and being a man, and even Bernie might have had a better shot because I think at least some white rage would have funneled into Bernie's anti-establishment economic shit in a general election.