Bolton

John Bolton said he would abide by a Senate subpoena. Why did he say that?

Most likely he said it in the same way I might say that I won't quit my teaching job to pitch for the Braves. He's making a commitment that will never be tested.  The Senate does not seem remotely ready to call witnesses. Bolton pointedly did NOT say he would abide by a House subpoena.  It would be interesting if the House did, in fact, subpoena him in the next couple of days.  My guess? He doesn't show.

Presumably, Bolton's statement puts some pressure on Senate "moderates" who might buck McConnell and write rules for the "fair trial" scenario. Here's a credible, central witness who should be heard, unless your desire is to sweep this under the rug.  However, who are these "moderates"? Mitt Romney will vote for the "fair trial." I could maybe see Mike Lee follow his lead, given how uniquely unpopular Trump is in Utah.

After that?

We can already write off Susan Collins.  She's the most worthless invertebrate in Congress.  Murkowski is more of a possibility, but I'm not holding my breath.  For the others, maybe a retiring Senator like Lamar Alexander or Johnny Isakson might support it, but there is equally no incentive for doing the right thing.  People like Joni Ernst, Cory Gardner or Martha McSally - who are running for re-election this year - are in a tight spot. Support the "fair trial" and you lose MAGAt support. Oppose it, and you lose independents. 

So, Bolton's offer to testify in a Senate trial is likely him trying to distance himself from the historical reckoning that is coming without jeopardizing his future in Republican politics.

It means nothing.