It shouldn't come as a surprise to you that Congress might launch a baseless investigation against a political opponent.

Also, just because the legal system drops a case does not mean there's nothing there. It can also mean they don't think they can get a conviction on the evidence. Private employers do their own investigations sometimes and will come to their own judgement about what their employee did or didn't do.

True, but you are aware that politicians are famous for wheeling and dealing, right? The quid pro quo could have been "resign and we won't release this".

The problem here is that you are making positive assertions of fact for things that are at best speculative claims.