President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE has reshaped his Cabinet and senior team dramatically in the first three-quarters of his presidency.

Over the past year, Trump has welcomed a new attorney general and defense secretary, a third legislative affairs director and a fourth national security adviser and has tapped a fifth person to head up the Department of Homeland Security.

He parted ways with his first secretaries of Labor and Energy and director of national intelligence, opening up a new series of vacancies that have since been filled in an acting or permanent capacity.

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Experts describe it as a record-setting turnover at the Cabinet and White House senior staff level in the first three years of the Trump administration.

“Trump’s management style is such that he seems to thrive in a world of very high turnover and new personnel,” said Kathryn Dunn Tenpas, a nonresident senior fellow at the Brookings Institution who researches White House staffing and turnover.

According to Tenpas’s research, 80 percent of the top positions in the White House have experienced turnover thus far in Trump’s first term in the Oval Office. Several positions have had multiple occupants, including White House chief of staff and press secretary.

“He’s had more turnover than all of his predecessors did after a full first term, and he achieved that in October,” Tenpas said.

White House allies argue that the higher rate of departures shouldn’t come as a surprise.

“He’s been a disrupter since day one, and he didn’t come to Washington with a group of hangers-on,” said Sean Spicer Sean Michael SpicerKellyanne Conway to leave White House at end of month Pro-Trump duo Diamond and Silk launch new program on Newsmax TV The Hill's 12:30 Report - Presented by Facebook - Supreme Court's unanimous decision on the Electoral College MORE, Trump’s first White House press secretary. “There’s just going to be a different dynamic than someone who has been in politics for a few decades.”

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Many of the dismissals and resignations have come in national security or foreign policy roles, including atop the departments of Defense and State.

Trump has found himself in disagreement with top advisers on foreign policy decisions, clashes that have led to various departures in the administration.

In September, Trump forced out John Bolton John BoltonThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE — his third national security adviser, known for his hawkish foreign policy views — after the two clashed over the president’s approach to issues such as North Korea and Afghanistan.

Trump replaced Bolton with Robert O’Brien, his former hostage negotiator, who friends predicted would would take a less confrontational approach to the senior position. O’Brien has appeared to gain standing with Trump quickly, representing the administration on a handful of important trips and recently accompanying the president and other aides to his Mar-a-Lago resort in Palm Beach, Fla.

The result, experts say, is a president less constrained by advisers who will push back on his “America first” agenda, such as Trump’s efforts to fulfill a campaign pledge to bring U.S. troops home from conflict abroad.

“Trump has over time succeeded in surrounding himself either with people of similar perspective on foreign policy or people who won’t stand up to him,” said Charles Kupchan, a senior fellow at the Council on Foreign Relations and former National Security Council aide during the Obama administration.

“Whether it’s positive or negative depends on whether you support Trump’s approach to foreign policy,” Kupchan said. “If you think America first is the right way to go, then having ‘yes men’ around the president is a good thing because Trump can be Trump. If you’re less comfortable with his foreign policy, then you’d rather see people pushing back.”

The impeachment hearings have illuminated Trump’s frayed relationship with and distrust of the national security bureaucracy.

When current and former officials — most career but some political appointees — testified about the administration’s unusual policymaking channel on Ukraine that involved Trump’s personal attorney Rudy Giuliani Rudy GiulianiJuan Williams: Breaking down the debates Giuliani criticizes NYC leadership: 'They're killing this city' More than 160 executives critique de Blasio's leadership amid pandemic MORE, Trump attacked some of them as “Never Trumpers,” sought distance from them or cast doubt on their statements.

The White House at one point dismissed the impeachment inquiry as “a coordinated smear campaign from far-left lawmakers and radical unelected bureaucrats waging war on the Constitution.”

One of the officials who testified, U.S. diplomat William Taylor, is set to leave his post at the start of the year, creating a vacancy at the U.S. Embassy in Ukraine.

The departures over the past three years aren’t limited to the foreign policy realm and have occurred for varying reasons. Alex Acosta Alex Alexander AcostaFederal litigator files complaint alleging Labor secretary abused his authority Appeals court to review legality of Epstein plea deal Appeals court finds prosecutors' secret plea agreement with Epstein didn't break law MORE resigned as Labor secretary in July amid controversy surrounding his handling of a 2008 plea deal with accused sex trafficker Jeffrey Epstein.

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Sarah Sanders Sarah Elizabeth SandersSarah Sanders on Trump's reported war dead criticism: 'Those comments didn't happen' Sarah Sanders memoir reportedly says Trump joked she should hook up with Kim Jong Un McEnany stamps her brand on White House press operation MORE, Trump’s second press secretary and a fierce Trump defender, stepped down at the end of June amid growing speculation she would mount a gubernatorial bid in her home state of Arkansas.

Often, Trump selects a candidate from elsewhere in the administration to fill a vacancy, which in turn leaves another role unfilled. That occurred when Trump tapped John Sullivan, then his deputy secretary of State, to replace Jon Huntsman as U.S. ambassador to Russia; the president then filled the No. 2 position with Stephen Biegun, his North Korea envoy.

The president has also tapped people to serve in high-level positions in an “acting” capacity, meaning they don’t go through Senate confirmation and are considered temporary occupants. It’s something he says gives him more “flexibility.” Chad WolfChad WolfDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Judge blocks some asylum restrictions, rules Chad Wolf serving as DHS secretary likely unlawful DHS asks Schiff to reconsider expanded probe after whistleblower complaint, declines additional interview requests MORE became the fifth official to hold the position as secretary of Homeland Security, and the third to do so in an acting capacity, in November.

Experts say the effect of such turnover on any administration would be disruption to the policymaking process. It takes time for new occupants to learn the functions of the job, and those serving in acting roles are not viewed as permanent employees, which creates uncertainty and hampers long-term planning.

“It’s highly inefficient,” said Tenpas.

But Spicer argued that the sum of the departures doesn’t matter to voters as long as Trump is seen as delivering on his agenda. He also said it’s difficult to judge the efficacy of one senior position holder compared to the next, given that each official can learn from his or her predecessor.

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“I think there’s some cases yes and there’s some cases maybe not,” Spicer said when asked if Trump was better off now than at the start of his administration with the people he has in place. “There are some people who are really good for right now.”

Senior officials in past administrations largely refrained from departing close to a presidential election, but that could be different under Trump. There is talk of Secretary of State Mike Pompeo Michael (Mike) Richard PompeoThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep Trump's foreign policy successes confound his detractors It's time for a Jackson-Vanik Amendment for China MORE running for Senate in Kansas and speculation that acting chief of staff Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE may leave at some point in the near future.

Politico reported recently that Mulvaney was expected to depart the White House sometime after the impeachment trial has ended. However, sources who spoke to The Hill downplayed the prospect of Mulvaney’s ouster.

“I won’t believe anything until it comes out of the president’s mouth,” said one source close to the White House.