James Mattis Donald Trump

(CNN) — Former Secretary of Defense James Mattis castigated President Donald Trump as "the first president in my lifetime who does not try to unite the American people" in a forceful rebuke of his former boss as nationwide protests have intensified over the death of George Floyd.

"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."

His pointed remarks follow more than a week of nationwide protests across the country calling for justice for Floyd, a black man who was killed last week by a white police officer in Minneapolis. In response, Trump earlier this week declared himself "your president of law and order" and vowed to return order to American streets using the military if widespread violence isn't quelled.

The comments from Mattis are a significant moment for a man who has kept mostly silent since leaving the administration. The retired Marine general had been pressed many times to comment on Trump, troop policies, the Pentagon, and other current events and had always refused because he didn't want to get involved and be a contradictory voice to the troops. Instead, Mattis always insisted he had said everything he wanted to say in his resignation letter.

And until a few days ago he had privately held to that view, but Mattis has become so distressed by the events of the last week that his views on speaking out changed.

The remarks will be a significant moment for many service members who idolize the former defense secretary, who — despite a career based on loyalty and respect for the military chain-of-command — is sending troops the message that the country can unite without the President's lead.

The message comes after days of increased military presence in Washington. National Guardsmen and federal law enforcement have been stationed around the nation's capital in a show of force not seen in recent memory. Federal law enforcement officers violently broke up peaceful protests in front of the White House on Monday, apparently so Trump could stage a photo-op at a church across the street from Lafayette Square, where protesters had gathered.

The former secretary, who resigned from Trump's Cabinet, also indirectly criticized current Defense Secretary Mark Esper's use of the word "battlespace" in reference to American cities.

"We must reject any thinking of our cities as a 'battlespace' that our uniformed military is called upon to 'dominate,' " Mattis said. "At home, we should use our military only when requested to do so, on very rare occasions, by state governors. Militarizing our response, as we witnessed in Washington, D.C., sets up a conflict — a false conflict — between the military and civilian society."

"It erodes the moral ground that ensures a trusted bond between men and women in uniform and the society they are sworn to protect, and of which they themselves are a part. Keeping public order rests with civilian state and local leaders who best understand their communities and are answerable to them."

Esper on Wednesday acknowledged his use of the word "battlespace" was not meant to indicate any conflict with Americans, but claimed he used a military term of art. Esper also specifically rejected the use of active duty forces in a law enforcement role at this time.

But Mattis directed most of ire at Trump saying "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."

Read Mattis' statement: