In a country fixated on which senior Trump adviser will be the next to get the boot, Lieutenant General H.R. McMaster's departure does not come as a major surprise. The United States' top advisor on national security had been on thin ice for an eternity in the Trump era of news cycles.

Thanking the president for his friendship, McMaster said he has filed a retirement request.

"After 34 years of service to our nation, I am requesting retirement from the US Army effective this summer, after which I will leave public service," McMaster said in a statement. "Throughout my career, it has been my greatest privilege to serve alongside extraordinary servicemembers and dedicated civilians."

Read more: John Bolton: The conservative hawk tapped by Trump

Ahead of the announcement, Nahal Toosi, who covers US foreign policy for the news organization Politico, said there had been speculation for months that Trump was going to fire McMaster. "[He] has been called the Schrödinger's Cat of national security advisers for months," she said, referring to the paradox in physics in which a cat in a box is considered both alive and dead.

Read more: Opinion: John Bolton's rise could be death knell for Iran deal

Drifting out of Trump's orbit and out of a job

McMaster and Trump were always an unlikely team in terms of style. McMaster is a career military officer and academic with a Ph.D. in military history, and Trump considers himself a straight-talking, convention-defying outsider.

McMaster and Trump reportedly clashed over policy in the past

The two also appear to have irreconcilable differences in terms of their personalities. Trump prefers casual banter to the orderly updates he received from his national security adviser. According to the Washington Post, which reported in mid-March that the president had told his chief of staff he was ready to sack McMaster, "The president has complained that McMaster is too rigid and that his briefings go on too long and seem irrelevant."

Read more: White House stability under john Kelly 'Depends on if people fall in lie or not'

Watch video 02:10 H.R. McMaster at MSC

McMaster had held his title since February 20, 2017 – far longer than most thought possible. So why is he out of a job now?

North Korea could be a factor. Trump credits his possible upcoming meeting with Kim Jong Un to his administration's tough military posturing. When asked why the North Koreans were potentially ready to come to the table, the US president answered: "Me."

Many critics of Trump's efforts at engagement believe it would be unwise to meet the North Koreans without setting clear terms for any negotiations. McMaster favored a particularly hardline approach.

"[McMaster] opposed any sort of talks with North Korea early on. He was really keen on putting this major pressure campaign almost to the point of bringing the North to its knees before the US was willing to talk to them," Toosi said.

Spring cleaning at the White House

McMaster's retirement comes amid a string of high-profile departures and rumors of a further shakeup among top US officials.

Several of those on their way out the door had tried to rein in Trump on certain issues. Trump's top economic adviser Gary Cohn announced his resignation in early March. A week later Secretary of State Rex Tillerson returned home early from an official visit to Africa after being unceremoniously sacked.

Read more: Opinion: With Tillerson's firing, White House loses a voice of reason

Little appears to be certain in Trump's White House, including whether Chief of Staff John Kelly will keep his job for long

Theories as to why Trump has been removing his top staff abound. Does he feel disempowered by Chief of Staff John Kelly's attempts to grapple with the reported chaos in the White House? Has he lost loyalists whispering in his ear and been left to trust his gut feeling? Or is he just feeling more confident in the second year of his presidency and seeking to reshuffle his inner circle to line up with him ideologically? It's crucial to take any analyses of Trump's motivations with a grain of salt. One of the few identifiable trends in his decision-making is the fact that he is a mercurial leader with erratic preferences.

One thing seems certain – Trump has been relishing the uncertainty gripping both his staffers and media pundits. He even joked about his love of the chaos at an annual dinner in March, saying, "The question everyone keeps asking is, 'Who is going to be the next to leave? Steve Miller or Melania?'"

'You're fired' — Trump administration casualties Dan Coats Director of National Intelligence Dan Coats resigned from his post, which oversees and coordinates all 17 US intelligence agencies, in July 2019. Coats clashed with Trump on Russia, taking a harder line on Vladimir Putin than the president. He also contradicted Trump's assertion that North Korea no longer posed a threat.

'You're fired' — Trump administration casualties Alexander Acosta Labor Secretary Alexander Acosta announced his resignation in July 2019, after criticism of a legal deal made years ago that led to financier Jeffrey Epstein only serving 13 months in jail for child sex abuse.

'You're fired' — Trump administration casualties Rod Rosenstein Deputy Attorney General Rod Rosenstein submitted his resignation at the end of April 2019, after a two-year run defined by his appointment of a special counsel, Robert Mueller, to investigate connections between Donald Trump's 2016 campaign and Russia. The move made Rosenstein a frequent target for Republican wrath and angry Trump tweets. Indeed, he often appeared to be on the edge of being fired.

'You're fired' — Trump administration casualties Randolph Alles Randolph Alles, a former Marine who reached the rank of major general, resigned as the head of the US Secret Service in early April 2019. Although initial news reports suggested he had been "fired," he later said he had been notified of changes to senior security positions and that he resigned voluntarily. He had previously served as acting deputy commission of US Customs and Border Protection.

'You're fired' — Trump administration casualties Kirstjen Nielsen Kirstjen Nielsen announced her resignation as secretary of homeland security in early April 2019. She had previously served in other administration positions, including deputy White House chief of staff. Nielsen, a hard-line border security advocate, is best known for her controversial policy of separating children from their migrant parents at the US border.

'You're fired' — Trump administration casualties Bill Shine Bill Shine announced his resignation as White House communications director in early March 2019. The former Fox News executive may be leaving his post, but he's not completely out of a job. The White House has said he will be working on Trump's 2020 reelection campaign.

'You're fired' — Trump administration casualties Brock Long Brock Long announced his resignation as the head of the Federal Emergency Management Agency (FEMA) mid-February 2109. Long is best known for managing the agency's response to historic wildfires in California and major landfalls of powerful hurricanes. However, his resignation came shortly after he was told to reimburse the government over the misuse of government vehicles.

'You're fired' — Trump administration casualties Brett McGurk Appointed by Trump's predecessor Barack Obama in 2015, McGurk was the US envoy to the coalition fighting "Islamic State" terrorists and was influential in shaping US policy in northern Syria. He was due to end his tenure in February 2019 but stepped down days after Defense Secretary Jim Mattis, largely due to Trump's sudden decision to take US soldiers out of Syria.

'You're fired' — Trump administration casualties Jim Mattis Defense Secretary Jim Mattis abruptly announced his retirement in late December 2018 after Trump ignored his advice and announced the complete withdrawal of US troops from Syria. Mattis' resignation letter laid bare the growing divide between them, criticizing his boss for his treatment of allies. Mattis was a keen supporter of NATO and traditional US alliances, putting him at odds with Trump.

'You're fired' — Trump administration casualties Ryan Zinke Interior Secretary Ryan Zinke resigned in December 2018 as pressure mounted from more than a dozen investigations into various aspects of his tenure and private business. The former Navy SEAL was a leading advocate of expanding domestic energy production, opening up vast swathes of the country for exploration.

'You're fired' — Trump administration casualties John F. Kelly In December 2018, Trump announced that John Kelly, his third chief of staff, would step down at the end of the year. He had been brought in to establish order in the Trump White House but found the job arduous, and his relationship with his boss soured. The retired four-star Marine Corps general was replaced by budget director Mick Mulvaney, after several candidates turned down the job.

'You're fired' — Trump administration casualties Jeff Sessions Attorney General Jeff Sessions was fired in November 2018 after several months of abuse from Trump. Despite being an early supporter, he attracted the wrath of his boss early on by recusing himself from the Justice Department investigation into collusion. He was replaced with a loyalist who shares Trump's concerns about the investigation.

'You're fired' — Trump administration casualties Nikki Haley United Nations Ambassador Nikki Haley, one of the administration's few high-profile women, announced her resignation in October 2018. She said her resignation was long-planned, but the announcement took most senior politicians by surprise. She lent international legitimacy to the administration as she attempted to provide a coherent message.

'You're fired' — Trump administration casualties Marc Short The White House director of legislative affairs announced he would leave his post effective July 20, 2018. Short, one of the administration's longest-serving members, was also one of its most visible, pushing Trump's legislative agenda on TV. But his work was frequently undercut by the president, who complained about deals the team had negotiated, preferring instead to go it alone without them.

'You're fired' — Trump administration casualties Scott Pruitt It remained a mystery to many how Pruitt could hang on for so long, but the president seemed to like him. Many on the left cringed at his every move as head of the Environmental Protection Agency. He was also embroiled in various ethics scandals. Nevertheless, Trump took to Twitter to thank Pruitt for doing an "outstanding job" at the EPA.

'You're fired' — Trump administration casualties Ty Cobb One of Trump's top lawyers in the ongoing special counsel investigation into Russian involvement in the 2016 presidential election, Cobb said he simply wanted to retire. But many believe he was forced out by Trump and others in his legal team for his lack of aggression in Robert Mueller's Russia probe. Cobb was said to have been increasingly uneasy about Trump's Twitter attacks on Mueller.

'You're fired' — Trump administration casualties Tom Bossert White House Homeland Security Adviser Tom Bossert, who had worked for George W. Bush, was reportedly pushed out in the shake-up that occurred after John Bolton replaced H.R. McMaster as national security adviser. It is said that Bolton had no issues with Bossert, but that he wanted his own team in place. The White House thanked Bossert for his "patriotic service" and wished him well.

'You're fired' — Trump administration casualties David Shulkin Though the White House said Shulkin resigned, he says he was fired. A holdover from the Obama administration, he was appointed to run the Department of Veteran's Affairs by Trump. His downfall came amid a travel expense scandal involving his wife. He criticized the atmosphere in the administration as "toxic, chaotic, disrespectful and subversive," claiming he was the victim of political intrigue.

'You're fired' — Trump administration casualties H.R. McMaster In a tweet on March 22, 2018, US President Trump announced he was replacing H.R. McMaster with John Bolton as his national security adviser. A respected general, McMaster said he would retire from the US army and public service. McMaster's departure was not a complete surprise, as he and Trump are reported to have had conflicting views on a number of US policies.

'You're fired' — Trump administration casualties Rex Tillerson A former Exxon executive, Tillerson had served as secretary of state for a little over a year. Donald Trump ousted Tillerson in order to form a "new team" ahead of talks with North Korea, adding that he and Tillerson "disagreed on things." The relationship between them is said to have deteriorated after Tillerson reportedly called Trump a "moron" in October 2017.

'You're fired' — Trump administration casualties Gary Cohn A Goldman Sachs veteran, Gary Cohn served as Donald Trump's top economic adviser at the head of the National Economic Council. He helped push through controversial tax reforms in 2017. However, Cohn stepped down in March 2018 after failing to persuade Trump to give up his idea of imposing tariffs on imported steel and aluminum.

'You're fired' — Trump administration casualties Hope Hicks Hope Hicks resigned from her post as the White House communications director in late February 2018. A day before resigning, she testified before US lawmakers on Russian interference. She admitted to telling "white lies" for Donald Trump, but not related to Russia. The White House insisted her resignation was not linked to the testimony. The 29-year-old was among Trump's closest aides.

'You're fired' — Trump administration casualties Rob Porter The White House staff secretary handed in his resignation after his ex-wives accused him of domestic abuse. Despite resigning, Rob Porter denied the allegations as "simply false." Trump initially defended Porter, and the US media questioned how Porter passed his background check for the job. Recently, reports surfaced of a romance between Porter and Trump's longtime aide Hope Hicks.

'You're fired' — Trump administration casualties Stephen Bannon He played a key role in getting Donald Trump into the White House, but even chief strategist Stephen Bannon was ousted within a year. Bannon was a champion of economic nationalism and Trump's "America First" strategy. After the fallout of white supremacist violence in Charlottesville mid-August, Bannon agreed to leave the administration.

'You're fired' — Trump administration casualties Anthony Scaramucci The 53-year-old former hedge fund investor nicknamed the "Mooch" was communications director for just 10 days. The colorful New Yorker filled a dream role that had been vacant for months, but was forced out on the same day that straight-shooting former Marine Corps general John Kelly became chief of staff. Trump was displeased with his infamous expletive-laden rant against other senior staff.

'You're fired' — Trump administration casualties Walter M. Shaub Jr. Walter Shaub, the former director of the Office of Government Ethics, resigned in July 2017 after clashing with the White House over Trump's complicated financial holdings. Shaub reportedly called Trump's administration a "laughingstock."

'You're fired' — Trump administration casualties Reince Priebus Reince Priebus, former White House chief of staff, was forced out just six months into his tenure after a public feud with Anthony Scaramucci, the White House communications director. Priebus was reportedly among those West Wing staffers who had opposed hiring Scaramucci.

'You're fired' — Trump administration casualties Sean Spicer Sean Spicer, who had a fraught relationship with the president and the press, resigned after telling Trump he vehemently disagreed with the selection of Anthony Scaramucci as White House communications director.

'You're fired' — Trump administration casualties Michael Dubke Michael Dubke, former White House communications director, was asked to leave in May 2017 over what was perceived as his poor handling of allegations of Russian involvement in the US election.

'You're fired' — Trump administration casualties James Comey US President Donald Trump fired FBI Director James Comey — allegedly over how he handled the Clinton emails investigation. Critics, however, believe the FBI's probe into Trump's campaign ties with Russia was the real reason.

'You're fired' — Trump administration casualties Michael Flynn Trump's national security adviser, Michael Flynn, resigned in February 2017 after revelations that he had discussed US sanctions on Russia with the Russian ambassador to the US before Trump took office, and then misled Vice President Mike Pence about the conversations.

'You're fired' — Trump administration casualties John Bolton US President Donald Trump fired his National Security Adviser John Bolton saying he disagreed "strongly" with his suggestions. Trump had tweeted that Bolton's "services are no longer needed at the White House."



DW editors send out a selection of the day's hard news and quality feature journalism. You can sign up to receive it directly here.