Senator Sanders seems aware of the problem. Lately, he’s argued that Republicans are the real socialists, since they provide corporate giveaways through tax breaks. He’s said that regular Americans have socialism already, in the form of Social Security and Medicare. He claims, without evidence, that socialism is so popular that it would bring out younger and low-propensity voters at unprecedented levels. And he has tried to append the meaningless modifier of “Democratic” to his “socialist” label…

To be sure, Donald Trump will call any Democratic nominee a “socialist”. But if it’s one of you, that charge will not stick, because it will be an obvious lie. You are Democratic capitalists. Your words, ideas, and histories are clear on this point, and voters will know it. By contrast, if Trump’s opponent is, as his team fervently hopes, a proud socialist, he will make the entire election – for president and for every other office on the ballot – a referendum on socialism. That is a fight that Democrats cannot win.

In this campaign – and in his 50 years in public life – Bernie Sanders somehow has skated past any serious, sustained scrutiny of his ideas and his record. Yet those are so extreme – so far outside the mainstream – that they simply must not be ignored during the remaining fight for the 2020 nomination. Either you will air and debate them now, and deny Sanders the nomination, or they will come roaring out of the Trump machine in the fall, when they will prove fatal.