The New York Times reports that the manuscript asserts several facts that, were they a part of any potential testimony Bolton would give in the Senate, could prove damaging to McConnell's efforts to bum-rush the end of the trial.
Via The Times:
President Trump told his national security adviser in August that he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats including the Bidens, according to an unpublished manuscript by the former adviser, John R. Bolton.
The Trump White House can't deny knowing about Bolton's assertions — they were previously sent the book to review.
Spoiler alert: Giuliani doesn't come off well in the book.