Its Russian money and misinformation support. Nothing else would rise to the level of corruption that we have seen. The whole Republican Party is infected with it. Super PACs full of dark money that giving talking points tied to campaign support.
I still believe Trump has some dirt on them he is holding over their heads. IMO, there isn’t much that could be worse than their cowardice since Jan 6 that places our Republic in serious peril - so whatever it is must be really embarrassing or really bad or both. Of course the cynic in me says they are just power hungry and that’s true but it still seems a stretch for me to believe they’d go this far unless there is something more he has on them.