As the war in Ukraine approached its first anniversary, the Pentagon’s top officer, Gen. Mark A. Milley, assessed the carnage that had followed Russia’s full-scale invasion: With more than than 100,000 soldiers likely killed or wounded on each side, he said, there was a “window of opportunity” for the combatants to hammer out a deal.

Milley told an audience in New York that both parties must recognize victory may not be “achievable through military means.” He drew a comparison to World War I, explaining how strategists a century earlier had predicted a swift end to the bloodshed, only for it to become an unwinnable standoff that killed millions and set the stage for World War II. “Things can get worse, so when there’s an opportunity to negotiate, when peace can be achieved, seize it,” Milley said. “Seize the moment.”

The declaration was classic Milley, according to colleagues and observers who have worked closely with him. The general, immersed in military history and alarmed by the potential for escalation with Russia, the largest nuclear power in the world, was publicly advocating a position the Biden administration had eschewed as the president and other top advisers sought to project unqualified support for Ukraine’s defense. It was a notion that unnerved America’s partners in Kyiv.

Milley, whose four-year tenure as chairman of the Joint Chiefs of Staff ends with his retirement this month, will exit center stage as one of the most consequential and polarizing military chiefs in recent memory, leading America’s armed forces through a fraught period that included the precarious final months of Donald Trump’s presidency, a disastrous withdrawal from Afghanistan and Washington’s high-stakes standoff with Moscow.

Admirers commend the brash Boston-area native for steering the military through Trump’s attempts to subvert democracy and the constitutional rule of law, keeping troops out of the 2020 election chaos and choreographing key aspects of the Pentagon’s support to Ukraine. Milley would say later he harbored concern that Trump might issue unlawful orders, and that, if he had, they “wouldn’t have been followed.”

Critics say the general stretched the bounds of what is expected to be a nonpartisan role, wading into hot-button debates again and again, and dragging the military further into the political fray at a time when the institution’s public backing is already under strain. Some found him overly focused on his own legacy.

This account of Milley’s tenure as chairman is based on interviews with more than a dozen senior political appointees in both the Trump and Biden administrations, retired military officers and other Washington insiders. Several people spoke on the condition of anonymity to offer frank assessments of the general’s record. Collectively, they portrayed an outspoken, ambitious leader who offended some in his assumption and stewardship of the military’s premier assignment, and who fell from favor with one president only to find new footing with another, all while navigating Washington’s toxic politics.

Milley, through a spokesman, declined to be interviewed for this profile.

Trump, apparently reacting to news coverage of the general’s impending retirement, said on his social media platform late Friday that Milley’s departure “will be a time for all citizens of the USA to celebrate!” He accused Milley of being a “train wreck,” and falsely stated that phone calls, authorized by Trump administration officials at the time, in which Milley sought to reassure Chinese officials that the United States was stable during the presidential transition were a “treasonous act.” Trump wrote, “This is an act so egregious that, in times gone by, the punishment would have been DEATH!”

Milley has not responded publicly to the allegations. He commented previously, though, that there is a “damaging drumbeat” of criticism directed at the Pentagon amounting to a “deliberate attempt, in my view, to smear the general officer corps and the leaders of the military, and to politicize the military.”

Like the general, retired Adm. Mike Mullen’s tenure as chairman of the Joint Chiefs of Staff, under Republican George W. Bush and Democrat Barack Obama, spanned two presidents with vastly different outlooks and agendas, the second of whom sought to undo much of what his predecessor had done. Under any circumstances, Mullen said, the job is “ridiculously hard.” Milley, he added, “had more of a challenge” than most and is likely to “come out somewhere close to heroic” for his actions during the presidential transition.

“He was, and remains, a hell of a warfighter,” Mullen said.

‘Milley wanted the job, obviously’

Milley, an Army infantry officer and former college hockey player, has spent over 43 years in the military and emerged as Trump’s selection for chairman at an unexpected time. The president announced his decision on Twitter, now called X, in December 2018, surprising senior officials at the Pentagon just before an Army-Navy football game. The move was months ahead of schedule and seen by many as undercutting the chairman at that time, Marine Gen. Joseph F. Dunford Jr., who was slated to remain in the position until the following September but seen by Trump as insufficiently loyal.

Jim Mattis, at the time Trump’s defense secretary, had recommended Gen. David Goldfein, the chief of staff of the Air Force, to succeed Dunford. Others close to the president suggested instead that he go with Milley, who had been recommended by Mattis to lead U.S. European Command. Milley knew Mattis wanted him in Europe, people familiar with the matter said, but accepted the role of chairman when Trump offered. “Milley wanted the job, obviously,” said one retired senior U.S. military officer. “Mattis will probably never talk to him again.” Mattis, who resigned later that month while citing differences of opinion with Trump, declined to comment.

Initially, Trump seemed enamored with Milley, whose tough talk and extensive combat record impressed the president, two former U.S. officials said. By all accounts, the general understood the president could be unpredictable and capricious. His mentors and colleagues had warned him that serving directly under Trump may be volatile and end poorly.

On a rainy September day in Washington, Milley was sworn into office. During the ceremony, he promised the president to “always provide informed, candid and impartial military advice to you, the secretary of defense, the National Security Council and to the Congress.” Trump, in his remarks, called Milley “outstanding” and said he was a “friend” who deserved the position.

Overshadowing the moment, though, were news accounts indicating that the president was the subject of a whistleblower complaint stemming from a phone call that he had with Volodymyr Zelenskyy, then the newly elected leader of Ukraine. The scandal would result in the first of Trump’s two impeachments.

In the ensuing weeks, Milley and the Pentagon were thrust into the spotlight amid a number of high-profile national security events. First, was the bloody incursion by Turkish forces into northern Syria, jeopardizing the safety of hundreds of American troops deployed there. Next came the daring raid to kill Islamic State leader Abu Bakr al-Baghdadi. By late December 2019, after an American contractor was killed in Iraq and the U.S. Embassy in Baghdad was breached, administration officials, having concluded Iranian-backed militias were responsible, hatched a plot to eliminate one of Tehran’s most celebrated military figures.

On Jan. 3, 2020, an American drone strike killed Qasem Soleimani, the head of the Iranian Quds Force, as he sat in a vehicle outside Baghdad International Airport. Milley and other U.S. officials defended the operation, saying intelligence had suggested that Soleimani was preparing to unleash a new wave of violence against U.S. personnel in the region. Iran responded with ballistic missile strikes against two American positions in Iraq, leaving dozens of troops with head injuries, but no fatalities.

Mark T. Esper, who became Trump’s defense secretary a few months before Milley took over the Joint Chiefs of Staff, wrote in his memoir that while some senior U.S. officials at the time wanted to strike Iran quickly and repeatedly, he and Milley urged restraint and consideration of second-order effects. In an interview, Esper, who clashed with Trump over a number of policy disagreements, called Milley “an important adviser and partner to me through an extraordinarily complex and difficult time in American history.”

Kenneth “Frank” McKenzie, the general responsible at that time for U.S. forces in the Middle East, said he has a “very, very, very high regard for Milley,” calling him “the only guy that stood by me” during some difficult days when, some feared, there was little standing in the way of a full-blown war with Iran. “I always felt Mark had my back up there in D.C. when nobody else was interested in doing that,” McKenzie said. Milley understood “the fact that moving forces in and out of the theater did send signals to Iran.”

‘I should not have been there’

In May 2020, after the police killing of George Floyd inspired racial justice protests in cities across the United States, Trump called for putting active-duty troops on America’s streets. But Milley and other senior defense officials saw great peril in any attempt to invoke the Insurrection Act, arguing instead that any violence should be addressed by law enforcement, not the military.

Weeks of tension finally boiled over on June 1, 2020, when law enforcement personnel abruptly and aggressively cleared hundreds of demonstrators gathered in Lafayette Square outside the White House, ahead of Trump and other officials marching to a church across the street in a show of force. Among them were Esper and, for a time, Milley.

The general, wearing his camouflage fatigues, broke off from the group shortly after Trump departed the White House, and later said that the situation came together so quickly that he did not initially realize what was happening. But the damage was done. Photographs of the spectacle caused a furor, with critics asserting that Trump had exploited the U.S. military to threaten the American people.

Milley considered resigning but was talked out of doing so by colleagues and others whose counsel he sought as he navigated Trump’s impulsive directives and desire to use the military to show political strength. Days later, the general issued an apology instead, telling an audience at the National Defense University in Washington that he had made a “mistake” and not realized what was happening until it was too late.

“I should not have been there,” Milley said. “My presence in that moment, and in that environment, created the perception of the military involved in domestic politics.”

The mea culpa, along with a similar one made by Esper, infuriated Trump to such a degree that neither man’s relationship with the president would recover. The two felt “hornswoggled” by the incident, according to a former U.S. official, after which both demonstrated greater independence from the White House.

For Milley’s part, he began a monthly campaign to underscore publicly that the military would take on no unconstitutional role in the looming presidential election or domestic politics more broadly. Speaking later to the House select committee that investigated the Jan. 6, 2021, assault by Trump’s supporters on the U.S. Capitol, he cited several media interviews he had granted in addition to comments he made at the National Museum of the United States Army in November 2020.

“We are unique among militaries,” Milley said then. “We do not take an oath to a king or a queen, a tyrant or a dictator. We do not take an oath to an individual. No, we do not take an oath to a country, a tribe or religion. We take an oath to the Constitution.”

Mullen, the retired Joint Chiefs chairman, said the Lafayette Square episode hurt both Milley and the military. “You better think through what your boundaries are before you start” a job like the chairmanship, he said, “because you’re going to get slammed. You’ll be in the Oval [Office] one day, and you’ve got 30 seconds. If you haven’t thought through what your boundaries are, you’re going to roll.”

‘Too much, too often and too loudly’

As President Biden took office, some Democrats wondered whether they could trust Milley, one of only a handful of senior U.S. officials due to stay on after the transition. The Biden administration, with its by-the-book national security process and deep bench of experienced Washington officials, would do business differently than its predecessors.

Milley earned trust along the way, observers said, advising Biden while not publicly disclosing their conversations. But under a sustained barrage of attacks from the former president and other conservatives, Milley continued to clash with critics.

One incident came during a House Armed Services Committee hearing in June 2021, as Republicans pressed Defense Secretary Lloyd Austin and Milley over what they called “wokeness” within the armed forces. They singled out an elective course on race being taught to cadets attending the U.S. Military Academy at West Point, N.Y., and a policy under Austin, implemented after dozens of military veterans participated in the Capitol riot, requiring all service members to spend a couple of hours learning about domestic extremism.

Milley told lawmakers he personally found it “offensive” that the military was being called out for “studying some theories that are out there.” The general said he wanted to “understand white rage” and what compelled thousands of people to assault Congress. “I’ve read Mao Tse Tung. I’ve read Karl Marx. I’ve read Lenin. That doesn’t make me a communist,” he added. “So what is wrong with” having “some situational understanding about the country for which we are here to defend?”

His statement went viral, becoming another example of Milley, in uniform, saying what critics believe would have been better left to a civilian political appointee. “One of the things about going to the Hill is, ‘Don’t say what you don’t have to say,’ ” said a retired general who worked with Milley. “Mark was trying to give an intellectual answer, but it didn’t work because the sound bites were bad.”

In August 2021, failures surrounding the fall of the American-backed government in Afghanistan and the subsequent deadly scramble to evacuate unleashed a torrent of criticism. Milley, who in private had advised Biden not to withdraw all forces as Taliban militants steadily advanced toward the Afghan capital, held his tongue as the president later falsely suggested that no one had encouraged him to maintain a presence of about 2,500 U.S. troops there. A month later, before the Senate Armed Services Committee, Milley declared the collapse a “strategic failure.”

“The enemy is in charge in Kabul,” testified Milley, who had served three tours in Afghanistan. “There’s no other way to describe that.” Milley, asked by Sen. Tom Cotton (R-Ark.) why he had not resigned after Biden chose not to follow his advice, replied that the United States “doesn’t want generals figuring out what orders we’re going to accept.”

A few months later, as the Kremlin telegraphed its preparations for the invasion of Ukraine, U.S. intelligence officials predicted incorrectly that Kyiv would fall quickly. Since then, Milley has cultivated what observers say is an effective partnership with his Ukrainian counterpart, Gen. Valery Zaluzhny, working adroitly to coordinate and sustain an expansive network of Western assistance that has enabled the outgunned Ukrainian military to inflict staggering losses on the Russians for nearly two years.

“I think he carried the department on Ukraine,” said McKenzie, the retired general. “If there was something close to an irreplaceable person, it’d be Mark Milley on Ukraine.”

The Milley era, observers say, is also unique for his participation in multiple books scrutinizing the Trump presidency, something he has acknowledged under questioning by members of the Senate Armed Services Committee. The accounts have cast him as a defender of American democracy in ways that are unhelpful to the nonpartisan nature of his job, critics say.

Kori Schake, an expert on civil-military relations at the American Enterprise Institute, said the general’s collaboration with authors appears to her as “self-aggrandizing.” She said she cringed reading accounts of Milley telling others they needed to safely “land the plane” while Trump worked to overturn his defeat in the 2020 election.

“It is not appropriate for the president’s senior military adviser to stray into what is political territory, and Gen. Milley does that a lot in his time as chairman,” Schake said. “He can’t resist the temptation.”

Another former senior defense official who worked with Milley was even more blunt. “He has a ton of virtues,” this person said, “but his Achilles’ heel will be that at times he spoke too much, too often, and too loudly, with himself usually the hero.”

His defenders say the general’s legacy is one of great consequence, as his tenure has overlapped with so many combustible moments in the nation’s history.

Peter Feaver, a civil-military relations expert at Duke University whom the general has consulted over the years, said that while there is a range of opinions about Milley and his execution of the job, he merits high marks. Yes, Feaver acknowledged, he made some mistakes. But critics have repeatedly exaggerated or miscast his actions, he said.

“Any time someone is painted in too vivid of colors, the chances are that the truth is somewhere in between,” he said. “General Milley had one of the toughest assignments” of “any chairman in modern memory.”

related stories

• Gen. CQ Brown confirmed as Joint Chiefs chairman as Senate works around Tuberville nominee hold