Sen. Bernie Sanders, I-Vt., has recently emerged as the front-runner in the Democratic presidential field. The rise of the progressive darling’s star also is coinciding with a barrage of television attack ads against him in the crucial early voting states of Iowa and Nevada.

Although the ads have been purchased by a super PAC called Democratic Majority for Israel, they make no mention of Sanders’ pro-Palestinian advocacy. Instead they take aim at Sanders’ perceived electability against President Donald Trump in a general election, arguing that a self-identified socialist is ill-equipped to take on Trump and highlighting Sanders' heart attack last year.

Still, the bulk of the political action committee’s funding comes from a group of high-profile political donors affiliated with the powerful American Israel Public Affairs Committee (AIPAC). The influential lobbying group has historically prided itself on bipartisanship. But its pushback against Sanders, coupled with its social media ads targeting congressional Democrats last month, reflects its growing concern over the pro-Palestinian faction within the Democratic party. 

The super PAC airing the anti-Sanders ads raised nearly $2.3 million for its war chest last year. An Al-Monitor analysis of Federal Election Commission filings shows that the vast majority of those funds — some $1.8 million — came from prominent AIPAC donors in November and December alone.