There are still quite a few pundits determined to pretend that America’s two great parties are symmetric — equally unwilling to face reality, equally pushed into extreme positions by special interests and rabid partisans. It’s nonsense, of course. Planned Parenthood isn’t the same thing as the Koch brothers, nor is Bernie Sanders the moral equivalent of Ted Cruz. And there’s no Democratic counterpart whatsoever to Donald Trump.

Moreover, when self-proclaimed centrist pundits get concrete about the policies they want, they have to tie themselves in knots to avoid admitting that what they’re describing are basically the positions of a guy named Barack Obama.

Still, there are some currents in our political life that do run through both parties. And one of them is the persistent delusion that a hidden majority of American voters either supports or can be persuaded to support radical policies, if only the right person were to make the case with sufficient fervor.

You see this on the right among hard-line conservatives, who insist that only the cowardice of Republican leaders has prevented the rollback of every progressive program instituted in the past couple of generations. Actually, you also see a version of this tendency among genteel, country-club-type Republicans, who continue to imagine that they represent the party’s mainstream even as polls show that almost two-thirds of likely primary voters support Mr. Trump, Mr. Cruz or Ben Carson.