The TLDR is that once upon a time, actually just a decade ago, AIPAC didn't have to spend a single dollar on primaries and now it does. There wasn't a pro-Palestine bloc, and now there is. There wasn't a truly viable pro-Israel alternative in J-Street, and now there is.
" The collapse of previous bipartisan consensus and discursive limits is a catastrophe for Israel’s position in the US in the long term. AIPAC did not spend directly on elections until 2021. They didn’t need to.".
You can tell how unpopular you are by how much money you have to spend to get folks to like you. See any rich kid arsehole or their patron saint, Elon Musk.