Here's the thing...
I like Bernie Sanders. Always have. The comparison with my country's own idol of the left - Jeremy Corbyn - is instructive. Corbyn is an incompetent buffoon. Sanders, by contrast, is a serious thinker on policy and a brilliant player of the political game. At another time, he might have made a great president. As it is, he's probably not going to get the chance.
But, like Corbyn, what he has managed to do is to energise people on the left - especially younger people - to get involved in politics. Where the prospects are much better for Sanders' legacy, however, is that his party can still win the election, and get a government into power that knows that progressive and socialist ideas have a significant level of popular support. If they continue to play it smart, Bernie and the people who support him can still wield significant influence here.
But not if Trump wins. If that happens, you've got another four years of the USA being made safe for nativist and reactionary populism. More racism. More misogyny. More overt criminality in office. More gerrymandering and vote suppression. The continual undermining of the rule of law will move on apace, with the rights of women, minorities, immigrants, and anyone who gets in Trump's way crushed mercilessly underfoot.
Anyone who thinks four years of that is worth it just so you don't have to hold your nose while voting (as I did for Corbyn) can, quite frankly, do one.