Trump’s national security adviser, H.R. McMaster, is out. It was a long time coming.

The embattled three-star general finally ends his rocky tenure at the White House — and especially with President Donald Trump.

Lt. Gen. H.R. McMaster began his tenure as national security adviser as one of the most celebrated military leaders of his generation. But President Donald Trump let him go him on Thursday after just over a year in the administration — leaving McMaster’s once-sterling reputation in tatters and the White House in even more disarray.

In a tweet, Trump announced that McMaster would make way for former UN Ambassador John Bolton, but that McMaster “will always remain my friend.” McMaster will retire from the military, according to the New York Times. Bolton will assume McMaster’s role on April 9.

“H.R. McMaster has served his country with distinction for more than 30 years,” Trump said in a statement. “General McMaster’s leadership of the National Security Council staff has helped my administration accomplish great things to bolster America’s national security.”

On March 15, the Washington Post reported that Trump decided to oust McMaster, but didn’t do so because he wanted to ensure there was a prominent successor in place and that McMaster has his next job lined up. But now Trump finally followed through.

McMaster follows closely behind Rex Tillerson, who Trump fired on March 13. Hours after Tillerson’s removal, McMaster told a reporter, “Hey, I’m still around.”

It wasn’t supposed to end this way. McMaster — along with Defense Secretary James Mattis and, at the time, Tillerson — was labeled an “adult” in the room whose military and strategic expertise would help him gain Trump’s trust and moderate the president’s most potentially dangerous foreign policy impulses.

Instead, McMaster soon found himself at odds with both the president and other top administration officials. Trump, for example, pushed back hard against McMaster on crucial national security decisions, particularly the decision to escalate the war in Afghanistan.

Trump also publicly lambasted McMaster for saying that the evidence Russia interfered in the 2016 presidential election was “incontrovertible” — a fact the president repeatedly denies. And McMaster also advocated for a more militaristic stance toward North Korea, consistently warning that time was running out before a potential war with Pyongyang.

But McMaster perhaps struggled most simply dealing with Trump. A National Security Council (NSC) staffer who worked with McMaster and is not authorized to speak publicly about internal matters told me that no policy decision Trump took was ever final until it was actually implemented.

In other words, it was hard for McMaster and his team to put a policy into place because the president’s wishes sometimes changed on a dime. That, in part, made it difficult for McMaster to simply do his job.

Plus, according to the Post, Trump didn’t like McMaster’s style: “The president has complained that McMaster is too rigid and that his briefings go on too long and seem irrelevant.”

“I can’t say that if another person was occupying the position right now, that they’d be doing a markedly better job,” Jake Sullivan, who was considered a lock to be Hillary Clinton’s national security adviser had she won the election, told me before the firing announcement.

Trump’s personal flaws aside, McMaster made errors of his own. For example, he publicly offered a widely scrutinized non-denial denial that Trump shared classified intelligence with Russians in the Oval Office.

So an Iraq War veteran who famously wrote that military advisers should speak truth to power and act honorably — especially when it was hard — lasted about a year in the Trump White House. Worse still, McMaster’s hard-earned reputation will be irreparably damaged by his association with Trump.

“With the possible exception of Henry Kissinger holding the NSC together while Nixon was flailing during Watergate, it would be hard to imagine a genuinely successful national security adviser with a failing president,” William Inboden, a top NSC staffer in the George W. Bush administration, told me. “The fate of the two are so linked.”

McMaster wasn’t Trump’s first pick

McMaster was not Trump’s first choice to be national security adviser. That was Michael Flynn, a retired three-star Army general who strongly supported Trump during the campaign. But after only 24 days in the role, Trump fired Flynn because he lied to Vice President Mike Pence about his communications with then-Russian Ambassador Sergey Kislyak after the election — a personnel move Trump still regrets having to make.

(Flynn pleaded guilty to lying to special counsel Robert Mueller’s probe into whether the Trump campaign colluded with Russia to win the 2016 presidential election.)

Trump then tried to lure retired Navy Vice Adm. Robert Harward, a Lockheed Martin executive, to take Flynn’s place. But Harward turned the offer down because the White House wouldn’t let him put his own team together. So the search continued until Trump heeded the advice of Armed Services Committee Chair Sen. John McCain (R-AZ), Sen. Tom Cotton (R-AK), and Mattis, who all said the president should pick McMaster.

“He’s a man of tremendous talent and tremendous experience,” Trump said during the unveiling of McMaster as his new national security adviser on February 20, 2017. “I watched and read a lot over the last two days. He is highly respected by everyone in the military, and we’re very honored to have him.”

McMaster was one of the few Trump appointments to draw praise from Democrats and Republicans alike. Sen. Jack Reed (RI), the top Democrat on the Armed Services Committee, said McMaster had “a reputation for courage and candor.” Bill Kristol, a conservative critic of the administration, tweeted “I can't imagine anyone better prepared for the challenges of being Trump's NSA than H.R. McMaster.” Michael McFaul, a former ambassador to Russia under President Barack Obama, tweeted “I have a lot of respect for H.R.”

The acclaim stemmed, in part, from McMaster’s image as a warrior-scholar. McMaster’s only book, Dereliction of Duty, is a bestselling history on the Vietnam War that concludes that President Lyndon Johnson’s military advisers should have pushed the administration harder to adopt their assessments and recommendations for the conflict. Had Johnson listened to them, McMaster argues, America might have done better in Southeast Asia. “The war in Vietnam was not lost in the field, nor was it lost on the front pages of the New York Times or the college campuses,” McMaster wrote. “It was lost in Washington, DC.”

Many inside and outside the White House expected that McMaster would get the National Security Council in order, work closely with other cabinet members like Mattis and Tillerson, and offer his unvarnished military advice to the president.

Early on, at least, McMaster offered some reasons for optimism. On April 5, 2017, just over a month into the job, he removed former top Trump aide Steve Bannon from the NSC — political aides haven’t historically been allowed to attend — and returned Director of National Intelligence Dan Coats and Chair of the Joint Chiefs of Staff Gen. Joseph Dunford to their historic roles as “regular attendees” of the gatherings.

The next day, Trump authorized a Tomahawk missile strike against a Syrian base that Bashar al-Assad had used to mount a chemical weapons attack against his own citizens; McMaster helped guide the decision-making process, which was widely praised. He also removed some of Flynn’s staff holdovers, most notably his then-deputy K.T. McFarland, who had drawn criticism for inexperience and acting as a partisan in a famously apolitical role.

But by May, internal squabbles started to play out in public. The biggest problem was McMaster recommended Trump send more troops to Afghanistan — advice that initially rankled many in the White House, most notably Trump himself.

Trump and McMaster didn’t see eye to eye on most things

Alex Wong/Getty Images

During a mid-July meeting, McMaster put forward a plan to send up to 3,900 new US troops to bolster the Afghan government in its flagging fight against the Taliban (at the time, there were about 8,400 American troops already in the country).

The meeting was a “shitshow,” according to a July 24, 2017, Politico report, as Trump rejected McMaster’s plan and “words were exchanged.” The president was wary of spending more blood and treasure in Afghanistan, especially when the US had lost around 2,400 troops and civilians since the war began in October 2001 and failed to deal a body blow to the Taliban. The extremist group controls, influences, or contests more than 40 percent of the country.

McMaster’s enemies in the administration, at the time led by Bannon, took advantage of Trump’s displeasure with McMaster’s Afghanistan proposal. They mockingly dubbed the fight in Central Asia as “McMaster’s War” and ruthlessly attacked the national security adviser during the Afghanistan debate to ruin his standing with the president.

“On policy, the faction of the White House loyal to senior strategist Steve Bannon is convinced McMaster is trying to trick the president into the kind of nation building that Trump campaigned against,” Bloomberg View’s Eli Lake wrote on May 8, 2017.

There’s no doubting that Trump was reluctant to deepen America’s involvement in what was already the longest war in US history. But on August 21, 2017, Trump took McMaster’s advice and ordered more US troops to Afghanistan — even though it went against his initial beliefs.

“My original instinct was to pull out — and, historically, I like following my instincts,” Trump told a military crowd at Fort Myer, which is near Arlington Cemetery. “But all my life I’ve heard that decisions are much different when you sit behind the desk in the Oval Office; in other words, when you’re president of the United States.”

Afghanistan wasn’t the only time Trump and McMaster were at odds. Last May, Trump said that South Korea would have to pay for the THAAD missile defense system, which Seoul wants to protect itself from North Korea’s ever-improving missile and nuclear programs. Trump promptly screamed at McMaster over the phone for contradicting him.

Trump was also expected to use a speech at NATO’s headquarters on May 25, 2017 to specifically endorse the alliance’s Article 5 provision, which calls for collective defense and says that an attack on any NATO nation is considered to be an attack on all of them. In advance of the speech, McMaster expected Trump to read language underscoring America’s support for Article 5. Instead, Trump omitted those 27 words, sparking new doubts about his commitment to the military alliance.

Trump also met with Russian President Vladimir Putin during last July’s G20 meeting in Hamburg, Germany, despite McMaster’s objections. While national security advisers usually attend those bilaterals, only Tillerson accompanied Trump.

And in February 2018, McMaster told an audience at the Munich Security Conference that Russia had meddled in the 2016 presidential election. “The evidence is now really incontrovertible and available in the public domain, whereas in the past it was difficult to attribute,” McMaster said in his remarks.

Trump quickly tweeted his displeasure with the comments, stating that “General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians.”

It also didn’t help that McMaster’s persistent chatter during meetings annoyed Trump, according to a New York Times report last May. During some of them, McMaster tried to correct or add color to what the president was saying — with Trump right there.

McMaster did have some successes, however. Besides the Syria strike, McMaster helped to guide Trump’s thinking about North Korea. He believed the US could not deter North Korean leader Kim Jong Un from continuing to expand his nuclear weapons program, and argued that the chance for war grew with each passing day. “We’re in a race, really, to able to solve this problem,” McMaster said during the last December’s Reagan National Defense Forum.

McMaster argued that the only way to change Kim’s mind was with the threat — and possible use — of military force. For months, rumors swirled that the administration had developed a plan for a so-called “bloody nose” strike. The plan was widely viewed as McMaster’s brainchild, although top officials deny that a “bloody nose” strike was ever an option.

But if the administration chooses to move forward with any military moves against North Korea, it will do so without McMaster in the White House.

“McMaster couldn’t keep riding the tiger”

No one questions McMaster’s intellect. The problem was he always seemed out of his depths as Trump’s top national security adviser. After all, he spent his life in the military and not much time dealing with Washington politics.

After Trump shared highly sensitive intelligence about an ISIS plot with top Russian officials on May 10, 2017, McMaster twice publicly defended the president’s actions. He didn’t deny that Trump had actually given that intelligence to an adversary and possibly put an Israeli spy — who was reportedly deep under cover in an ISIS cell — in danger.

Instead, McMaster claimed what Trump did was “wholly appropriate” and even acknowledged that Trump didn’t know where the intelligence he shared came from. That’s not something a seasoned political hand says to explain away why the president made a potentially costly mistake.

McMaster later spoke during a June 28 Center for a New American Security conference in a keynote address. Trying to defend Trump’s foreign policy is tough enough. But McMaster’s insistence that Trump’s criticism of European allies stemmed from “tough love” sparked literal laughter from the crowd.

Michele Flournoy, the event’s moderator and a well-respected national security professional, pushed back on the comment. “I can tell you that they are not feeling very loved at the moment,” she said, prompting more laughter. “They’re feeling the tough part, but not the love part.”

McMaster also helped write two stunningly partisan op-eds on the administration’s purported policy accomplishments, which raised eyebrows because uniformed military officers are supposed to strictly stay clear of politics. His co-author was Gary Cohn, Trump’s then-top economic adviser, who resigned earlier this month.

The two men defended the president’s first foreign trip to the Middle East and Europe in the Wall Street Journal on May 30, 2017, claiming Trump’s presence and actions showed just how willing America was to work with allies and partners. That was the same trip where Trump refused to commit to NATO’s Article 5, alarming key US allies around the world.

And in the July 13, 2017, New York Times piece, they argued America’s foreign policy was going well, and that Trump got what he wanted out of the G20 meetings. But that’s not how many who tuned into the gathering saw it. Putin outplayed Trump when the Russian leader got the president to accept his narrative that Moscow didn’t interfere in the election. The Weekly Standard, a conservative magazine, even called it a “diplomatic depantsing.”

So while serving Trump is surely difficult, understanding McMaster’s downfall would be incomplete without noting that the general — as talented as he is — made some critical mistakes along the way.

“Unless an adviser’s policy recommendations and administrative style coincide with the president’s own immediate emotions and interests, there is great potential for conflict,” Bartholomew Sparrow, who wrote a book about former National Security Adviser Brent Scowcroft, told me. “There was an accumulation of serious differences in substance and process to make the relationship unsustainable. McMaster couldn’t keep riding the tiger.”

McMaster’s time as national security adviser may not have amounted to a dereliction of duty, but the general definitely didn’t meet the standards he had set for others. Future historians may be as critical of McMaster as McMaster was of the disgraced generals who led the US to defeat in Vietnam.