Harry Dunn, who endured racist abuse while serving as a U.S. Capitol police officer during the insurrection on Jan. 6, 2021, fell short on Tuesday in his bid for the Democratic nomination in Maryland’s 3rd Congressional District.

Maryland state Sen. Sarah Elfreth defeated Dunn — and a host of less formidable candidates — with critical help from the American Israel Public Affairs Committee, whose super PAC spent more than $4.2 million boosting her bid. Those funds, which materialized in April, helped Elfreth offset Dunn’s direct fundraising advantage. While Elfreth’s campaign denied that she’d courted AIPAC specifically, her campaign had invited outside support, flagging points super PACs should make about her on a webpage that was later deleted.

Elfreth is now the prohibitive favorite to represent the suburban Baltimore/Washington, D.C.-area seat in Congress. The district is solidly Democratic and historically not competitive in general elections.

Elfreth is likely to legislate as a mainstream liberal. She ran as a champion of abortion rights and gun safety measures, priorities she has backed in the state’s Democratic legislature.

“My top priority is delivering for this community,” she says in a TV spot, before listing off some of her union endorsements.

Dunn’s defeat is a victory for right-leaning pro-Israel groups, and it highlights the ability of a single, well-funded super PAC to radically disrupt a congressional race, even when its intended target is a folk hero. This election cycle, as Israel’s invasion of Gaza has divided the Democratic Party, the super PAC spending of AIPAC and like-minded pro-Israel groups has been more pivotal in Democratic House primaries than outside money from virtually any other sector.

It is still not entirely clear why AIPAC backed Elfreth over Dunn. The group’s super PAC, United Democracy Project, told HuffPost in April that while it saw Dunn as an ally, it viewed Elfreth as the “stronger candidate” to defeat other, less Israel-friendly candidates in the crowded Democratic field.

Dunn’s stances on domestic policy are somewhat more progressive than Elfreth’s. Unlike Elfreth, Dunn has come out specifically in support of Medicare for All and renounced corporate PAC donations. But he mostly campaigned on protecting democracy from Republican authoritarianism of the kind he witnessed on Jan. 6, as well as the corruption he sees as an extension of that same threat.

In a Israel policy paper obtained by HuffPost, a now-standard feature of contemporary Democratic congressional campaigns, Dunn opposes putting stricter conditions on U.S. aid to Israel. He even demurred when asked by HuffPost to weigh in on President Joe Biden’s recent decision to halt a weapons transfer to Israel.

But lawmakers’ policy views are shaped, in part, by their electoral coalitions. AIPAC’s opposition helped turn Dunn’s candidacy into a progressive rallying cry that might have given him greater influence once he reached Washington. The progressive pro-Israel group J Street endorsed Dunn in late April and the Congressional Progressive Caucus PAC backed him earlier this month.

Indeed, Dunn, who might have been ripe to become an AIPAC ally, turned on it when it began spending against him, blasting the group for receiving massive contributions from Republican donors and for endorsing House Republicans who had voted against certifying the 2020 presidential election. (A single-issue group, AIPAC has also endorsed top Democrats, including Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries, both of New York.)

“Candidates who receive this support accept the endorsement of an organization that has backed candidates and members of Congress who incited the rioters I fought on January 6th and tried to overthrow our democracy,” Dunn said in an early April statement that set the tone for his criticism of Elfreth, which he hammered home in a TV ad.