If the Democratic establishment is panicking at the prospect of the party nominating a socialist for president, Republicans are snickering. But there’s a certain amount of playacting on both sides. Mr. Trump has signaled that he wants to run against Mr. Sanders, and many Trump supporters believe that the Vermont senator would lose in a rout. But that’s wishful thinking. For starters, the socialist label is less toxic than it once was, which means that beating Bernie will involve a lot more than name-calling…

Democrats who are worried about a socialist at the top of the ticket probably won’t stay worried for long. Republicans who once obsessed over Bill Clinton’s character flaws were willing to look past Mr. Trump’s. Conservatives who once championed free-trade policies were willing to defend Mr. Trump’s trade wars. Because the political right has no monopoly on inconsistency, and because partisans are more interested in winning than in ideological purity, expect similar behavior in defense of Mr. Sanders.

The reality is that Democrats have been moving in Mr. Sanders’s direction for some time. What he’s offering the country is truth in advertising, and if he becomes the nominee, the media and political left will rally to his defense. Liberal commentators will explain away his past kind words for the Soviet Union, Cuba and Nicaragua’s Sandinistas, who wowed him with “their intelligence and their sincerity.” Those who can’t quite bring themselves to defend Mr. Sanders directly will instead train their fire on his critics. Be prepared for the anti-anti-Bernie brigades.