For a third time during Donald Trump’s presidency, his top defense chiefs have spoken out during a moment of upheaval, issuing a memo to troops describing the violence at the U.S. Capitol as “sedition” and “insurrection” and affirming that Joe Biden is the incoming president.

In an internal memo that was unusual for military leaders who traditionally try to avoid commenting on anything related to politics, the top uniformed officers of each military branch reminded troops of their sworn duty to protect the constitutional process and transition of power.

It was signed by Chairman of the Joint Chiefs of Staff Army Gen. Mark Milley and all of the members of the Joint Staff.

The Capitol came under attack on Jan. 6 by pro-Trump rioters who surged past security and broke into the building while members of Congress were in the process of certifying the Electoral College votes that won the election for Biden against Trump.

“We witnessed actions inside the Capitol that were inconsistent with the rule of law. The rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection,” Milley and all of the other service chiefs wrote.

Former Defense Secretary Chuck Hagel, who led the Pentagon under President Barack Obama, said having the Joint Staff come out so forcefully was unprecedented.

“We are living through something this country has never, ever lived through before,” Hagel told McClatchy in a phone interview.

He said that during his tenure memos from all of the Joint Chiefs were rare and focused on internal policy changes, “nothing remotely similar to what the Chiefs sent out” on Tuesday.

The “violent riot,” the Joint Chiefs statement said, “was a direct assault on the U.S. Congress, the Capitol building and our Constitutional process.”

It noted that on Jan. 20, Biden “will be inaugurated and become our 46th Commander in Chief.”

The military’s top uniformed leadership likely felt the need to speak out among “reports some of the violent mob that attacked Congress were flashing military IDs, the visibility of veterans among the insurrectionists, and members of Congress wanting individual soldiers guarding the inauguration vetted for insurrectionist sympathies,” said Kori Schake, a former Defense Department and National Security Council official who is now the director of foreign and defense policy studies at the American Enterprise Institute.

“They (the service Chiefs) don’t want the idea to take hold that good order and discipline are insufficient, so they’re reminding everyone of their oath and apolitical commitment. It’s a good thing,” Schake said.

A former Defense official who previously worked for the Pentagon’s senior leadership said “before 2016, a statement such as that from the Joint Chiefs of Staff would have been highly unusual, if not tectonic, in its impact.”

Last June, after the military came under criticism for its role in clearing out protesters near the White House who were protesting the death of George Floyd in police custody, Milley and former Defense Secretary Mark Esper both sent memos to the troops reminding them of their sworn duty to the Constitution.

In 2018, former Defense Secretary James Mattis, in his final message to the armed forces after he resigned in protest over deep policy disagreements with Trump over the country’s NATO alliances and the president announcing he was withdrawing troops from Syria, said, “I am confident that each of you remains undistracted from our sworn mission to support and defend the Constitution.”

In the memo on Tuesday, the Joint Chiefs also told the military to hold fast to their oath.

“As service members we must embody the values and ideals of the nation,” the chiefs wrote. “We support and defend the Constitution. Any act to disrupt the Constitutional process is not only against our traditions, values and oath, it is against the law.”

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