Mark T. Esper on Monday became the third Defense secretary under President Donald Trump to depart office amid controversy and the latest in a long line of administration officials that Trump has dismissed.

Trump made the announcement in a tweet Monday, stating that Christopher C. Miller, the director of the National Counterterrorism Center, will serve as acting secretary and then saying: “Mark Esper has been terminated. I would like to thank him for his service.”

The dismissal of Esper introduces a major new element of uncertainty and chaos into U.S. national security during a transition between presidents that was already roiled by Trump’s refusal to concede his election loss and his dissemination of baseless charges that the election was fraudulent.

Republicans were silent on Trump’s actions in the immediate aftermath. Mac Thornberry of Texas, the top Republican on House Armed Services, issued a statement praising Esper’s service without a mention of Trump or the timing of the firing. Senate Armed Services Chairman James M. Inhofe, R-Okla., briefly mentioned Trump in his own statement, but did not address the circumstances surrounding Esper’s firing or the transition period.

Democrats, however, quickly blasted the president’s action.

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House Armed Services Chairman Adam Smith, D-Wash., called Esper’s firing “destabilizing” and said it is “imperative that the Pentagon remain under stable, experienced leadership during the transition of power.

“President Trump’s decision to fire Secretary Esper out of spite is not just childish, it’s also reckless,” Smith said. “It has long been clear that President Trump cares about loyalty above all else, often at the expense of competence, and during a period of presidential transition competence in government is of the utmost importance.”

Virignia Democrat Mark Warner, vice chairman of the Senate Intelligence Committee posted a similar warning to Twitter.

“This president can still do a lot of damage between now and January. We can’t take our eyes off the ball yet,” Warner said. “Secretary Esper deserves our thanks for his service. And our country deserves better than this.”

Retired Adm. James Stavridis, the former commander of U.S. forces in Europe, tweeted that the firing “makes no sense,” especially at this time.

“Things are already unstable internationally, and this does not help. We need to try and create stability in transition time — Hopefully opponents will not try and take advantage,” Stavridis said.

Esper had been the confirmed secretary since July 2019.

Rumors had swirled in recent days and weeks that Esper was on the outs with Trump. But Esper’s fate may have been sealed as far back as June 3, when he publicly split with the president over whether active-duty U.S. troops were needed to fight lawlessness amid protests over the killing of George Floyd in Minnesota.

On June 1, law enforcement personnel in Lafayette Square across from the White House violently dispersed peaceful protesters.

That same day, Trump said he might soon have to invoke the Insurrection Act, which would be the legal prerequisite for deploying active-duty U.S. military personnel to quell domestic disturbances.

Two days later, Esper told reporters he would not support such a move at that time.

“The option to use active-duty forces in a law enforcement role should only be used as a matter of last resort and only in the most urgent and dire situations,” Esper said. “We are not in one of those situations now. I do not support invoking the Insurrection Act.”

As Esper spoke, about 1,600 active-duty military personnel had been moved to Washington, D.C., to be in position to assist police and National Guardsmen.

Esper had initially wanted to send the regular forces back to their bases, but he later reversed that order. The reversal came after his comments about the Insurrection Act had triggered speculation that his job was in jeopardy.

Kayleigh McEnany, Trump’s press secretary, was asked that day if Trump still supported Esper.

“As of right now, Secretary Esper is still Secretary Esper, and should the president lose faith, we will all learn about that in the future,” she replied.

“The president has the sole authority to invoke the Insurrection Act,” she noted. “It is definitely a tool within his power.”

From lobbyist to ‘secdef’

Esper had been at the Pentagon’s helm during a resurgence of defense spending and as the department attempted to reorient itself toward “great power competition” and next generation technologies and away from counterterrorism.

In 2020, though, his job was dominated by the challenge of dealing with the coronavirus pandemic and ultimately with military support for police during nationwide protests for racial justice.

Esper had been Army secretary before Trump tapped him last year for the Defense secretary job.

Previously, Esper had been a lobbyist for defense contractor Raytheon. His earlier career included stints as an Army officer, a congressional staffer, a Heritage Foundation chief of staff and an executive at the Aerospace Industries Association.

Tumultuous tenures

Trump’s first Pentagon secretary, retired Marine Corps Gen. James Mattis, also became a part of the recent debate over the use of the military in law enforcement.

Mattis, who had been discreet in his criticism of Trump since leaving office a year and a half ago, broke from that practice on June 3, when he published a critique in which he said Trump “does not even pretend to try” to unify the country.

Mattis had been Defense secretary for almost the entire first two years of the administration and resigned in protest on Dec. 20, 2018, over his concern about Trump’s announced withdrawal of U.S. troops from Syria and the president’s disdain for traditional alliances.

After Mattis submitted his resignation, he had planned to stay on for two months, until late February, but Trump replaced him on Jan. 1, 2019 with the deputy secretary, Patrick Shanahan.

Trump had been embarrassed and angered by Mattis’s resignation letter, which was an oblique critique of what Mattis considered Trump’s disregard for U.S. allies.

Shanahan, an erstwhile Boeing executive, then stepped into the job on an acting basis for a half year after Mattis’s departure.

But Shanahan had to step aside from consideration as the nominee after disclosures that his sometimes violent family disputes had been holding up his FBI background check.