But the problem goes beyond Sanders supporters. Rank-and-file Democrats, as a whole, are significantly more pro-socialist than independents are. And while Republicans, conversely, are more anti-socialist than independents are, the gap between Democrats and independents, on average, is about 10 points bigger than the gap between Republicans and independents…

Why are Americans more likely to refuse (or, at least, to tell pollsters that they refuse) to vote for a socialist than for a woman or a Muslim? Probably because socialism isn’t an innate characteristic or a matter of personal faith. It’s a doctrine about how government should intervene in the lives of other people. That makes it a legitimate reason to vote against a candidate and therefore—unlike race, sex, or religion—a legitimate factor when you’re considering whether to nominate a candidate other voters won’t support.

This chasm endangers Sanders in a general election against Trump. In an ABC/Washington Post poll taken last summer, Biden led Trump in a hypothetical matchup by 10 points. Other potential Democratic nominees tied Trump or barely led him. Sanders held a one-point lead among independents and among voters as a whole. But when respondents were asked to choose between Trump and “a Democratic candidate who you regard as a socialist,” the numbers shifted. Democrats, by a margin of 82 percent to 8 percent, said they’d support the socialist. Independents, given the same choice, went for Trump, 50 percent to 42 percent. With their support, Trump beat the hypothetical socialist, 49 percent to 43 percent.