Sources for this post:

TikTok video showing what offices of Congressmen look like - thank you, aptly named u/GamingTheSystem-01

Guardian article which states that over $20 million was spent, but the link used as evidence does not specifically name AIPAC as the source.

The New York Times article on the matter does.

Now, in barely a month, an AIPAC-affiliated super PAC has spent $14.5 million — up to $17,000 an hour — on the race, filling television screens, stuffing mailboxes and clogging phone lines with caustic attacks. With days to go, the expenditures have already eclipsed what any interest group has ever spent on a single House race. (...)

The paid messages almost never mention Israel. In Mr. Bowman’s race, they have favored attacks aimed at the party’s base portraying the congressman as a pariah who “keeps attacking President Biden” and courts “controversy, chaos and conspiracy.” (...)

“Assuming the outcome is as we expect it, the message is going to be that being pro-Israel is not just wise policy, it’s smart politics,” said Mark Mellman, a Democratic pollster whose Democratic Majority for Israel spent $1 million against Mr. Bowman. (...)

Mr. Bowman, who represents a large Jewish population, presented himself as the ideal target. Although he condemned Hamas’s Oct. 7 attack, he was among the first lawmakers to call for a cease-fire in Gaza, to accuse Israel of committing genocide there and to push to curtail American military aid to Israel — positions that AIPAC directly opposes. (...)

Many cite information published by news media that Democratic Majority for Israel now says it uncovered. The group said it paid researchers who found blog posts and videos showing Mr. Bowman dabbling in conspiracy theories about Sept. 11 and praising a writer many Jews consider an antisemite, then shared them with reporters. (Mr. Bowman has apologized, and says he is not prejudiced against any group.)

The writer in question is Norman Finkelstein, an obvious antisemite....