After Representative Cori Bush, Democrat of Missouri, became the second member of the left-wing “squad” to lose her re-election bid, she placed the blame for her defeat solely on one organization: the American Israel Public Affairs Committee.

“All they did was radicalize me, so now they need to be afraid,” Ms. Bush said in a fiery speech after her loss on Tuesday evening.

“AIPAC, I’m coming to tear your kingdom down!” she shouted.

The pro-Israel organization made no secret of its plans to target Ms. Bush, who had opposed providing Israel with funding for the war in Gaza. Through a political action committee, the group pumped more than $8 million into the race.

On Tuesday, its investment paid off: Wesley Bell, the St. Louis County prosecutor who aligned himself with Israel, defeated Ms. Bush in the Democratic primary as voters in the district rallied behind him.

“Last night, Wesley Bell, a pro-Israel progressive, achieved a consequential victory over an incumbent anti-Israel detractor,” said Marshall Wittmann, a spokesman for AIPAC. “Once again, a progressive pro-Israel Democrat has prevailed over a candidate who represents the extremist fringe that is hostile to the Jewish state.”

It was the second time in recent months that AIPAC has played a critical role in a Democratic primary race. In June, another candidate backed by AIPAC, George Latimer, the Westchester County executive, defeated Representative Jamaal Bowman of New York, another squad member who had opposed providing funding to Israel for the war.