According to a report by the Washington Examiner, Mattis' book talks about his time as the leader of U.S. Central Command, when he repeatedly warned the Obama administration about Iran and Sunni Islamist terrorists. According to Mattis, during that time Iran posed the “more deadly of the two threats.”

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Obama allegedly fired Mattis because of these warnings--and making matters worse, the administration didn’t even tell him about the Iranian plot to bomb the café. Mattis was only later filled in about the plot by an officer in Florida who told him about a press conference held by Eric Holder and Robert Mueller about the arrest of two Iranians who had planned the attack. The targeted establishment, called Café Milano, is a "high-end restaurant in Washington that was a favorite of the rich and famous, including Saudi Arabia’s ambassador, Adel al-Jubeir," according to the Examiner.

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Mattis writes in his book, "Attorney General Eric Holder said the bombing plot was ‘directed and approved by elements of the Iranian government and, specifically, senior members of the Qods Force.’ The Qods were the Special Operations Force of the Revolutionary Guards, reporting to the top of the Iranian government."

If the bomb had gone off, it would have been the "worst attack on us since 9/11."

He wrote, "Had the bomb gone off, those in the restaurant and on the street would have been ripped apart, blood rushing down sewer drains. It would have been the worst attack on us since 9/11. I sensed that only Iran’s impression of America’s impotence could have led them to risk such an act within a couple of miles of the White House. Absent one fundamental mistake — the terrorists had engaged an undercover DEA agent in an attempt to smuggle the bomb — the Iranians would have pulled off this devastating attack. Had that bomb exploded, it would have changed history."

Mattis wanted the US to "respond forcefully," but Obama would not inform the public about how serious the threat was. Mattis wrote, "We treated an act of war as a law enforcement violation, jailing the low-level courier."

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Then came the bombshell--Mattis' suspected reason for Obama's weak response: "In my view, we had to hold Iran to account and strike back when attacked. But there was a reason for the administration’s restraint: The administration was secretly negotiating with Iran, although I was not privy to the details at the time."

Those negotiations eventually became the Iran Deal. President Trump withdrew the US from the deal in 2018.