Kelly Jane Torrance of the Washington Examiner highlights interesting details from the memoir of former U.S. Defense secretary Jim Mattis.

Though former Defense Secretary Jim Mattis mentions his last boss, President Trump, only in the opening pages of his new book, the Washington establishment seems certain the tome on leadership is directed at him, with one observer calling it “mainly a 100,000-word subtweet.”

Mattis says he won’t discuss a sitting president, though it seems clear he disdains Trump’s leadership style. But he is scathing about a former president in Call Sign Chaos: Learning to Lead, which is released today, and he doesn’t hesitate to name him: Barack Obama.

The former general’s opinion of Obama, for whom Mattis was head of U.S. Central Command from 2010 until 2013, might be summed up by single entry in the book’s index: “Obama, Barack, strategic thinking lacking.”

That entry points readers to a couple of the book’s most thoughtful passages on the necessity of allies and the dangers of alienating them. Those who have heard Mattis in his publicity campaign emphasize these points assume he’s speaking indirectly of Trump: for example, his disparagement of NATO. But Mattis makes clear in Call Sign Chaos that he believes Obama bungled Middle East policy and, as a result, sent American allies around the world a dangerous message.

Mattis summarizes his time commanding CENTCOM, overseeing military operations in the Middle East and Central Asia until Obama fired him, in harsh terms: “It was to be a time when I would witness duty and deceit, courage and cowardice, and, ultimately, strategic frustration.”