"As the book nears publication and details spill out, many congressional Democrats quickly assailed Mr. Bolton for not telling his story during the impeachment proceedings and instead saving it for his $2 million book."

"Mr. Bolton explains his position in the epilogue, saying he wanted to wait to see if a judge would order one of his deputies to testify over White House objections. Once the House impeached Mr. Trump over the Ukraine matter, Mr. Bolton volunteered to testify in the Senate trial that followed if subpoenaed. But Senate Republicans voted to block new testimony by him and any other witnesses even after The New York Times reported that his forthcoming book would confirm the quid pro quo. Some of those Republican senators said that even if Mr. Bolton was correct, it would not be enough in their minds to make Mr. Trump the first president in American history convicted and removed from office. Mr. Bolton blames House Democrats for being in a rush rather than waiting for the court system to rule on whether witnesses like him should testify, and he faults them for narrowing their inquiry to just the Ukraine matter rather than building a broader case with more examples of misconduct by the president. 'Had a Senate majority agreed to call witnesses and had I testified, I am convinced, given the environment then existing because of the House’s impeachment malpractice, that it would have made no significant difference in the Senate outcome,' he writes."
From "Five Takeaways From John Bolton’s Memoir 'The Room Where It Happened' describes Mr. Bolton’s 17 turbulent months at President Trump’s side through a multitude of crises and foreign policy challenges" by Peter Baker (NYT).

ADDED:

Wacko John Bolton’s “exceedingly tedious”(New York Times) book is made up of lies & fake stories. Said all good about me, in print, until the day I fired him. A disgruntled boring fool who only wanted to go to war. Never had a clue, was ostracized & happily dumped. What a dope!

— Donald J. Trump (@realDonaldTrump) June 18, 2020