Same thing they did when the NRA tried to play bothsides; create party rules to ban party members from taking money from them.
AIPAC is the single biggest donor of GOP money into Democratic races, they are spending millions right now to unseat people like Jamaal Bowman and replace them with right-wingers like George Latimer. It’s in the party leadership’s interest to put a stop to that. Allowing this right-wing influence into the Democratic party is how we end up with conservative obstructionsts like Manchin.