Representative Jamaal Bowman of New York, known for his vocal progressivism in Congress, suffered a significant defeat in the primary on Tuesday, as reported by The Associated Press. He was overwhelmed by an unprecedented campaign funded by pro-Israel groups and hindered by several avoidable mistakes.

Mr. Bowman lost to George Latimer, the Westchester County executive, in what became the most contentious intra-party battle of the year and the costliest House primary in history.

The conflict initially centered on Mr. Bowman’s criticism of Israel’s actions against Hamas last fall. However, it escalated into a broader struggle reflecting deep divisions within the Democratic Party concerning issues of race, class, and ideology in the diverse district encompassing parts of Westchester County and the Bronx.

Mr. Bowman, the district’s inaugural Black congressman and a dedicated democratic socialist, remained steadfast in advocating for a Gaza cease-fire and progressive economic agendas. Despite trailing in polls, he consistently accused his white rival of racism and vehemently criticized pro-Israel groups as a “Zionist regime” attempting to sway the election through financial influence.

National progressives rallied behind Mr. Bowman’s stance on the war and economic issues, spurred by Representative Alexandria Ocasio-Cortez of New York in a last-ditch effort. However, their efforts failed to sway skeptical voters and only strengthened opposition to him.

A super PAC associated with the American Israel Public Affairs Committee, a pro-Israel lobby, poured $15 million into defeating Mr. Bowman, marking the largest expenditure by an outside group in a House race.

In contrast, Mr. Latimer, a moderate with strong local support, appealed to voters seeking a return to traditional Democratic policies. Centrists and Jewish voters gravitated towards his candidacy. Meanwhile, Mr. Bowman faced criticism for a series of missteps, including pulling a false fire alarm in a House office building last fall, which further alienated potential supporters.

The outcome was decisive. With 59 percent of the votes tallied, Mr. Latimer led with 55 percent compared to Mr. Bowman’s 45 percent.

Due to the district’s strong Democratic leaning, Mr. Latimer is anticipated to secure a straightforward victory in the general election. At 70 years old, he would rank among the oldest House freshmen and is expected to align reliably with party leadership.