The Senators were probably blindsided because the WH figured by the time anything came out from his book the trial would be over, don't forget, they're trying to wrap this all up before SOTU and Bolton's book isn't supposed to be released until early March. As you all have previously stated, Trump doesn't give a sh*t about any of them.
What I'm interested in seeing is whats going to ultimately happen to his defense lawyers because either Purpura or Cipollone would be part of the team who would have to review and ok the transcript prior to publishing to ensure there is no classified info in it. That means they are standing before the Senate with full knowledge of what Bolton would say in testimony.