What an incredible thing to watch Senator Bernie Sanders rail against the idea of open immigration into America. His own father, a Jewish immigrant from Poland, and his own mother, who was born in America to Jewish parents, were here because of America’s capacious immigration policy. Yet when Mr. Sanders sits down with a reporter of Vox and is asked about the idea of sharply increasing immigration even to the level of open borders, he gets his back up and tries to palm off the idea as “right wing.”

“No, that’s a Koch brothers proposal,” snaps the only socialist in the American senate.

“Really?” asks the incredulous interviewer, Ezra Klein, the editor of Vox, in one of the most wonderful exchanges of the campaign.

“Of course,” Mr. Sanders sneers. “That’s a right wing proposal which says essentially there is no United States. . .”

“But it would make …” Mr. Klein starts to say.

“Excuse me . . .” Mr. Sanders growls, trying — and failing — to cut him off.

“It would make a lot of global poor richer, wouldn’t it?” asks Mr. Klein, not to be interrupted.

“It would make everybody in America poorer,” the senator snarls. “You’re doing away with the concept of a nation state.”

It is such a whirlpool of ignorance that we don’t know where to start. But let’s start with the fact that the hunger for more immigration into America is not a confection of the Koch Brothers, however heroic they may be. It is one of the enumerated reasons for our declaring independence from the British tyrant, George III. The Declaration complained that George “has endeavoured to prevent the population of these States; for that purpose obstructing the Laws for Naturalization of Foreigners; refusing to pass others to encourage their migrations hither.”

Does Senator Sanders not know this? Immigration is not a Koch Brothers scheme. It is a scheme of the patriots who pledged their lives, fortunes, and sacred honor to create our revolution. Mr. Sanders, of all people, should know that it also happens to have been a cause of the American socialists, particularly Meyer London, the second socialist ever elected to the Congress. London, whose portrait still hangs in the offices of the Jewish Daily Forward in Lower Manhattan, was an early opponent of immigration restrictions being brought in early in the 20th century.

Meyer London spoke on immigration on the floor of the congress in the fight over restrictions in 1921. He argued that immigration was self-regulating, and spoke the famous sentence: “The extraordinary and unprecedented growth of the United States is as much a cause as the effect of immigration.” He warned against the brewing immigration restrictions intended, he foresaw, to be what he called permanent exclusions. He said: “To prevent immigration means to cripple the United States.” The only Socialist in Congress today should be ashamed of himself.

Good for Vox for nailing him on the point. We were alerted to it, incidentally, by the Future of Capitalism Web site. The Vox scribe who wrote up the Sanders interview, Dylan Matthews, recalled that one proponent of at least the principle of open borders was Robert Bartley, now gone alas but then the editor of the Wall Street Journal, which today is the most eloquent tribune of a free market, welcoming immigration policy. Let us see now what Secretary Clinton and the Democrats will do with the question on which Bernie Sanders has blundered on a scale with Donald Trump.