President Trump began the day Wednesday with his current defense secretary undercutting his suggestion to dispatch active-duty military to quell unrest across the country. And he ended it with his former defense secretary rebuking his entire presidency.

Jim Mattis broke his silence Wednesday in an extraordinary written statement to the Atlantic. The statement marks the most significant rebuke of Trump to date from a former member of his administration — both because of the content and because of Mattis’s stature.

In the letter, Mattis makes clear that his criticism of Trump has been building for some time. But although he resigned after a disagreement over Trump’s planned troop withdrawal from Syria and later suggested it wasn’t helpful for military men like himself to speak out against the commander in chief, he suggested the display Monday — in which law enforcement cleared peaceful protesters from Lafayette Square near the White House to make way for a photo op — was his breaking point.

“When I joined the military, some 50 years ago, I swore an oath to support and defend the Constitution,” Mattis said. “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.”

The episode has earned widespread criticism and notably caused Mattis’s successor, Defense Secretary Mark T. Esper, to distance himself from the display. In remarks since Monday, Esper has said he didn’t know he would be roped into a photo op with Trump at a church near the White House and acknowledged the importance of military leaders appearing apolitical. Esper on Wednesday also distanced himself from Trump’s proposal to invoke the Insurrection Act, which would allow the use of active-duty military forces to combat the unrest over the killing of George Floyd in Minneapolis.

Mattis even singled out Esper in his statement, albeit without using his name. “We must reject any thinking of our cities as a ‘battlespace’ that our uniformed military is called upon to ‘dominate,’ ” Mattis said. These are terms Esper had used Monday in a call with governors.

But the bigger target of Mattis’s comments was Trump, whom he accused of being divisive — not just because of who he is, but because that’s Trump’s goal, Mattis said.

“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 said. “We are witnessing the consequences of three years of this deliberate effort. We are witnessing the consequences of three years without mature leadership. 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; to past generations that bled to defend our promise; and to our children.”

Mattis also called Trump’s decision to clear the square an “abuse.”

“We know that we are better than the abuse of executive authority that we witnessed in Lafayette Square,” he said. “We must reject and hold accountable those in office who would make a mockery of our Constitution. At the same time, we must remember Lincoln’s ‘better angels,’ and listen to them, as we work to unite.”

Mattis is not the first former member of Trump’s administration or even his Cabinet to criticize him. Former secretary of state Rex Tillerson at one point said that Trump was “undisciplined, doesn’t like to read,” and that people around him had to prevent him from breaking the law. Former White House chief of staff John F. Kelly has criticized Trump’s attitudes and many of Trump’s signature efforts: In February, Kelly said that Trump’s request of Ukrainian President Volodymyr Zelensky to investigate Joe Biden and his son amounted to an “illegal order.” Former Trump national security adviser John Bolton also set himself up as a potential impeachment witness against Trump on the Ukraine situation, though he ultimately did not testify.

Mattis’s comments, though, are the most significant yet — by virtue of who he is, what he said and the post he held. He’s not the only general — Kelly is also one — nor is he the only top Cabinet official — another being Tillerson.

But Mattis combines both of those things, and he was, before his departure, one of the rare uniting figures of the Trump administration. A 2018 poll showed that 59 percent of Americans approved of his performance as defense secretary, compared with just 22 percent who disapproved. The only other polled official who has compared to those numbers was former U.N. ambassador Nikki Haley.

Mattis’s comments are also significantly more severe than any of the others. While they criticized Trump’s leadership style and priorities on the job, Mattis is attacking his character and his very essence.

Trump’s opponents have long been waiting for someone around Trump to speak out in truly unvarnished terms about the president, thinking it might spur others to muster the courage to do the same. We should hardly expect Mattis’s comments to create such a sea change. But if anyone could do it, it might be Mattis.

This post has been updated.