Senator Bernie Sanders, the progressive former presidential candidate who rose to prominence in part by denouncing the influence of wealthy interests in politics, has a new target in his sights: the American Israel Public Affairs Committee and its affiliated super PAC, which is spending heavily in Democratic primaries for the first time this year.

After Mr. Sanders traveled last week to Pittsburgh to campaign for Summer Lee, a liberal state legislator whose House campaign was opposed by millions of dollars in such spending, he is now headed to Texas. There, he is aiming to lift up another progressive congressional candidate, Jessica Cisneros, whose left-wing challenge of a moderate incumbent has been met with significant spending from the pro-Israel super PAC.

“This is a war,” Mr. Sanders said in an interview, “for the future of the Democratic Party.”…

“Why would an organization go around criticizing someone like Summer Lee for not being a strong enough Democrat when they themselves have endorsed extreme right-wing Republicans?” Mr. Sanders said. “In my view, their goal is to create a two-party system, Democrats and Republicans, in which both parties are responsive to the needs of corporate America and the billionaire class.”