Could Bernie Sanders have beaten Donald Trump? I think there's almost no chance of that, but since the topic keeps coming up, I feel like I ought to explain why. I know this won't persuade anyone, but the reason is simple: He's just too liberal.
Here's a chart of every Democratic presidential candidate in the postwar era—plus Bernie Sanders. It shows them from least liberal to most liberal. I used NOMINATE to gauge how liberal senators were; this paper to fill in the governors; and a bit of personal judgment to shift a few candidates around. I'm not pretending I got this perfect, but I think it's in the ballpark. Feel free to move folks around if you like.
Very roughly, the scores show how the candidates compare to all of Congress: LBJ was more liberal than two-thirds of Congress, while Bernie Sanders is more liberal than 99 percent of Congress. Winning candidates are in red.
No Democratic candidate with a score below 15 has ever won the presidency. Bernie Sanders, needless to say, is way below 15. There's not a snowball's chance that he could have won the presidency.
Like I said, I don't expect this to persuade anyone. You can always make up a dozen reasons why this time would have been different. But it wouldn't have been. In the end, Trump was treated like an ordinary Republican. Hillary Clinton, after being forced a bit to the left during the primaries, was treated like an ordinary Democrat who was right on the bubble of being too liberal for the country. Both candidates had plenty of personal flaws that they used against each other, but Sanders did too. They were just different than Clinton's. Republicans would have twisted him up like a wet rag and tossed him down the drain.