President Trump continued his rhetorical offensive against former Secretary of Defense James Mattis Thursday, tweeting a letter purportedly written by his former attorney John Dowd that attacked Mattis for criticizing Trump's response to ongoing protests.

The letter knocks Mattis' military service and suggests he let "hack politicians" abuse his reputation. Dowd, a retired Marine Judge Advocate who Trump called "a Super Star lawyer," served as Trump's lead counsel in the Russia investigation before resigning in March 2018.

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"I slept on your statement and woke up appalled and upset," Dowd wrote. "You lost me. Never dreamed you would let a bunch of hack politicians use your good name and reputation-earned with the blood and guts of young Marines. You did what you said you [wouldn't] -- engage in this discourse. Marines keep their word."

In a statement to The Atlantic Wednesday, Mattis said he was "angry and appalled" at the death of George Floyd following his arrest by Minneapolis police May 25.

"Donald Trump is the first president in my lifetime who does not try to unite the American people — does not even pretend to try," Mattis said. "Instead, he tries to divide us ... We are witnessing the consequences of three years of this deliberate effort. We are witnessing the consequences of three years without mature leadership."

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Mattis also strongly objected to authorities' decision to clear away protesters in Washington D.C.’s Lafayette Park on Monday before Trump's visit to the historic St. John’s Church, which rioters had burned the previous night.

“When I joined the military, some 50 years ago,” Mattis wrote, “I swore an oath to support and defend the Constitution. 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 letter from Dowd forcefully pushed back on that narrative, telling Mattis that the protesters were "terrorists" who "were abusing and disrespecting the police ... Marines support the police in harm's way."

Dowd's letter was met with mockery on Twitter, with many poking fun at Trump for turning to his former lawyer for help. Others mocked Dowd himself.

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Trump, Dowd said, was right to challenge governors over their allegedly weak response to urban riots.

"No one divided the country more than [former President] Obama," Dowd writes. "He abandoned our black brothers and sisters. He gave guns to the cartels," he added, apparently referring to the "Fast and Furious" scandal. "He apologized for our precious sacrifice and generosity overseas. You remember, he fired you.

"President Trump has done more to help our minority brothers and sisters in three years than anyone in the last fifty," Dowd went on. "Ask the black pastors. Ask the leaders of the black colleges and universities. He got them funded. Ask them about prison reform which ended the draconian sentences imposed on young black men by the laws enacted by [Joe] Biden and his hacks[.] You need to bone up on your homework and stop listening to Uncle Leon," he added in an apparent reference to former Defense Secretary Leon Panetta.

"I understand," Dowd continued, "you had to stick to the assigned narrative which did not include three years of corrupt investigations and evidence to destroy this President his office, and his lawful free election. Nancy [Pelosi] has no tolerance for dissent in the ranks- [sic] including those with stars."

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Dowd also jabbed Mattis for not taking out Iranian General Qassem Soleimani, asking, "Why did it take President Trump to have the instinct and balls to take him out?"

Trump's former attorney went on to suggest that Mattis was angry at Trump because of "embarrassment for your own failure as the leader of Central Command."

Dowd did not immediately respond to Fox News' request for comment.