Ronald Kessler’s new book, “The Trump White House: Changing the Rules of the Game,” is trustworthy, and, in an unusual twist these days, it’s favorable to the president. “Because of the liberal bias of the mainstream media,” Kessler writes in a poker tell as obvious as any ever seen, “many of Trump’s achievements are either underplayed or not reported at all.” Kessler doesn’t underplay them, and overstates some, but gets almost everything down — good and bad — of Season One of the Trump presidency. Among Trump’s triumphs, Kessler points to the two most significant: the seating of Supreme Court Justice Neil M. Gorsuch, and the massive tax cut and tax reform bill. Kessler also got Trump to sit down for an interview on New Year’s Eve at Mar-a-Lago, a conversation that shows the president confident and comfortable in his role.

I checked with one of Kessler’s sources, who is quoted quite liberally, and discovered that indeed the source spent time with the author. The source hadn’t read the book yet but the voice he projects in the pages sounds right to me. Thus, Kessler’s note-taking or tape-recording seems reliable, which is an odd but increasingly necessary assessment to include in a book review, but we are in an era when facts and sources are sometimes elusive. Kessler’s book seems to me professional and ethical, a workmanlike, useful contribution to the accumulating pile of source material on this presidency (beginning of course with the tweets. All of them. Pity Trump’s Caro).