Re the Dannehy resignation.
So far as I can tell, there is no "validated" explanation. She sent a short email to colleagues in Conn with the announcement and no reason. Speculation is she's not happy with what might be about to happen.

But that is the "easy" speculation that lines up with what the press wants to be true, so it's easy to put that out with just a thin reed of support.
Here's an alternative just as plausible.

Dannehy is a 1986 Harvard Law Grad. That puts her in her like between 59-61 years old. She started with DOJ in 1991. She left at the end of 2010 to become Dep. AG of Conn. She rejoined Durham in March 2019 for his investigation.

Dep. AG of Conn, is the No. 2 position -- it's a policy job, not a courtroom job.
Durham's investigation to date has been in the "investigation" stage. That is very different than the courtroom stage.

By putting in the 18 months she has, she has likely gone over 20 years federal service time -- which she might not have had when she left in Dec. 2010 to become Dep. AG of Conn since she joined DOJ in 1991 -- 19 years earlier.

If indictments are coming, that is a commitment of another 18-24 months minimum if she was going to stay with the case until completed -- unlike the senior SCO prosecutors who all left with cases still pending.

So this might be nothing more than someone who has already put in a long career -- and how is 10 years removed from having tried cases in federal court -- saying "Someone else is a better candidate for trying these cases than I am."

She has spent her entire legal career making $150-200k a year tops. Maybe she has a private practice job lined up at 3x that, and thinks "I've got 10 years left".
That was my thinking when I left -- every year I stayed at $170,000 was one less year at a larger amount.