Former Defense Secretary James Mattis on Wednesday slammed President Donald Trump’s response to the protests over the death of George Floyd, saying the president “tries to divide us” while also calling his “bizarre photo-op” in front of St. John’s Episcopal Church “an abuse of executive authority.”

“Donald Trump is the first president in my lifetime who does not try to unite the American people — does not even pretend to try. Instead, he tries to divide us,” Mattis wrote in a statement published by the Atlantic.

“Instructions given by the military departments to our troops before the Normandy invasion reminded soldiers that ‘The Nazi slogan for destroying us … was ‘Divide and Conquer.’ Our American answer is ‘In Union there is Strength.’ We must summon that unity to surmount this crisis—confident that we are better than our politics, Mattis wrote.

In the stunning rebuke of his former boss, the former general noted that he’d sworn to defend the Constitution when he was sworn into the Marine Corps “some 50 years ago.”

“Never did I dream that troops taking that same oath would be ordered under any circumstance to violate the Constitutional rights of their fellow citizens — much less to provide a bizarre photo op for the elected commander-in-chief, with military leadership standing alongside,” Mattis wrote, referring to Monday night’s federal show of force to clear protesters from the front of the White House.

After they were cleared, Trump walked across Lafayette Park with Defense Secretary Mark Esper, Army Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, and others to pose for a picture with a Bible in front of the church, which had been damaged in a riot the night before. The photo-op came minutes after Trump announced he was prepared to call in the military to handle unruly protesters around the country.

“We do not need to militarize our response to protests. We need to unite around a common purpose,” Mattis wrote.

Trump, he said, is a divider, and the country is “witnessing the consequences of three years of this deliberate effort.”

“We can unite without him, drawing on the strengths inherent in our civil society. This will not be easy, as the past few days have shown, but we owe it to our fellow citizens,” Mattis wrote.

Mattis resigned in December of 2018, suggested in his resignation letter that Trump was not treating allies with respect and had not been “clear-eyed” about U.S. enemies and competitors. The president, he said, should have a defense chief who shares his views.

He told the Atlantic last year he had no plans to speak out against the administration, saying “you need to give the people who are still there as much opportunity as possible to defend the country.”

But, he added, “There is a period in which I owe my silence. It’s not eternal. It’s not going to be forever.”

That period came to an end this week.

“I have watched this week’s unfolding events, angry and appalled. The words ‘Equal Justice Under Law’ are carved in the pediment of the United States Supreme Court. This is precisely what protesters are rightly demanding,” Mattis said.