Good morning. If you're wondering what all this talk is about John Bolton's book, Jonathan Chait summarizes it pretty well. The whole Trump defense hinges on there not being one witness who testified under oath that they heard Trump give the order that Ukraine was not to get the money (or a few other perks) until they announced an investigation into the corruption of the Bidens so Trump could cite that as evidence the Bidens were corrupt.
It's doubtful any of Trump's defenders thought he didn't give that order. They were just clinging to the legal point that no one testified under oath that they'd heard him give it. But it turns out that John Bolton is willing to testify under oath and in Bolton's as-yet-unpublished book, Bolton said, yes, he heard Trump give that order. So now it comes down to trying to prevent him from testifying.
Might work. Trump has a way of "winning" by technicalities, not actual victories…you know, like "winning" the presidency (and an alleged clean mandate) without actually getting the most votes. But if they do block Bolton or other witnesses who might be equally destructive to their case, they'll "win" on a technicality, not because there was an actual finding of the truth. No wonder one of O.J. Simpson's lawyers felt comfortable joining the team.