If you really want to know what former National Security Adviser John Bolton though of President Trump's actions regarding Ukraine, you may not have to rely on the Senate to call him as a witness in the president's upcoming impeachment trial.

That's because Bolton is going to reveal some of what he saw in his upcoming book, people familiar with the matter told The New York Times. The book, which is almost finished, is reportedly going to detail Bolton's time in the White House, events related to Russia and Venezuela, and his interactions with other administration officials, some of whom reportedly don't come across very well, including former U.S. Ambassador to the United Nations Nikki Haley, Secretary of State Mike Pompeo, and acting White House Chief of Staff Mick Mulvaney.

The Ukraine scandal, which is at the center of Trump's impeachment, will fill at least some pages, too, and Bolton is expected to share some of his observations about Trump's efforts to pressure Ukrainian officials into announcing an investigation into former Vice President Joe Biden's son, Hunter.

Bolton has said he's prepared to testify should the Senate issue a subpoena, but it's unclear if the upper chamber will do so. Read more at The New York Times. Tim O'Donnell