Will Bernie Sanders learn the lessons of the Jewish-American socialists who came before him? He’s soaring in the polls at the moment, but he seems oblivious to those on whose shoulders he seeks to stand. That could cost him as he seeks to convert his campaign from a protest vote on the margins to a broader challenge to the leadership of a Democratic Party that has long since come un-moored from the principles of FDR, JFK, LBJ, and, despite Hillary’s campaign, Bill Clinton.

This came into focus, at least for me, in the interview the senator gave to Ezra Klein, editor of a new, liberal website called Vox. Klein sprang on Sanders over the question of immigration, asking him about the idea of open borders. Sanders replied by trying to dismiss the idea of radically increasing immigration as a “right-wing” scheme. He called it a “Koch brothers proposal.” Klein reacted with incredulity. “Of course,” Sanders says. “That’s a right-wing proposal.”

Sanders asserted that open immigration “says essentially there is no United States.” He failed to address the fact that immigration was one of the reasons for the American secession from Britain, enumerated in the Declaration of Independence itself. It complained that the British tyrant King George III “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.”

The American founders were, in today’s terms, decidedly right wing. They believed in markets, limited government, and private property. Modern, free market conservatives have emerged in the van in the struggle to maintain, and expand, America’s welcoming spirit. The most famous tribune of this has been the Wall Street Journal, which in 1984 issued a famous editorial suggesting that, in theory at least, it would support a constitutional amendment saying there shall be open borders.

(Days after the Journal published that editorial, I had brunch with Isaac Bashevis Singer at the Brooklyn apartment of the editor of the Yiddish Forward, Simon Weber. When I brought up the Journal editorial, Singer exclaimed, “What, all those Mexicans!” I said I couldn’t believe I was hearing such a remark in the home of the editor of the Forward, at which point Si Weber beckoned me out onto his balcony, shook his finger at me, and said, “I know you guys from the Wall Street Journal, you just want cheap labor!”)

What was so astonishing about Senator Sanders’ anti-immigration tirade to Vox (and for that matter, Si Weber’s scolding of me) was the seeming obliviousness to the American socialists who came before. Sanders’ most famous forerunner, Meyer London (who, after Wisconsin’s Victor Berger, was the second socialist elected to the United States Congress) gave one of the great immigration speeches ever delivered in Congress. It was in 1921, when Congress was gearing up to sharply curb immigration.

London, who won his election with the support of the Forward, argued that immigration was self-regulating. “The extraordinary and unprecedented growth of the United States is as much a cause as the effect of immigration,” is the way he put it. He warned that “to prevent immigration means to cripple the United States.” How bizarre it is to hear Senator Sanders arguing that opening up immigration “would make everybody in America poorer.”

Immigration isn’t the only head on which Senator Sanders might want to brush up on his American socialist history. There’s also Israel. It proved to be one of the things that undid Meyer London. He represented in Congress a district teeming with Yiddish-speaking garment workers, and at one point was asked to introduce a resolution in support of the Balfour Declaration. London brushed the demarche aside, saying: “Let us stop pretending about the Jewish past and let us stop making fools of ourselves about the Jewish future.”

Nearly a century later, Sanders has rebuffed the major American Zionist organizations and Jewish defense agencies who are opposing the Iran appeasement. U.S. Secretary of State John Kerry had barely finished announcing the pact when he and U.S. President Barack Obama were congratulated by Sanders, who called the deal “a victory for diplomacy over saber-rattling and could keep the United States from being drawn into another never-ending war in the Middle East.” No doubt the parallels are inexact, but the fact is that Meyer London’s failure of vision is widely credited with costing him the election of 1918.

Seth Lipsky, the founding editor of The Forward and a former foreign editor of The Wall Street Journal, is editor of The New York Sun.