For much of his tumultuous tenure, US President Donald Trump has made impulsive, gut-level pronouncements - about dealing with Democrats on immigration, tearing up the Iran nuclear deal or supporting stricter gun control - only to be walked back by his more cautious staff.

Those days, it appears, are over.

In the past two weeks, Trump has directed tariffs on steel and aluminum imports over the fierce objections of his top economic adviser and agreed to an unprecedented meeting with North Korea's dictator despite concerns from national security aides.

Today, Trump fired Secretary of State Rex Tillerson who had forged a tight working relationship with Defence Secretary Jim Mattis to try to rein in some of Trump's most impetuous decisions.


"I made that decision by myself," Trump told reporters at the White House. Though he was talking about North Korea, it is a mantra that has never rang truer in his nearly 14 months as leader.

Trump's moves have shaken and alarmed a West Wing staff who fear the President has felt less restrained about acting on his whims amid the recent departures of several longtime aides, including communications director Hope Hicks and staff secretary Rob Porter.

Trump's personal assistant John McEntee, who had served from the earliest days of his campaign, was fired after losing his security clearance, further depleting the ranks of those the President feels he can trust.

White House allies in Washington suggested Trump has been liberated to manage his Administration as he did his private business, making decisions that feel good in the moment because he believes in his ability to win - regardless of whether they are backed by rigorous analysis or supported by top advisers.

This, they said, is the real Trump - freewheeling by nature, decisive in the moment, unafraid to chart his own course.

"He's running the White House like the Trump organisation," said one person close to the President, describing Trump as increasingly at the centre of command in White House decision-making and checking in on the status of various projects by the hour.

While Chief of Staff John Kelly is running operations, the ally said Trump is taking a more hands on approach to everything from political messaging and strategy to the management of the Cabinet.

Other people who have worked with Trump in the past said his recent moves are an indication he is concerned with the state of his presidency.

"When he's under pressure is when he tends to do this impulsive stuff," said Jack O'Donnell, former president of the Trump Plaza Hotel and Casino in Atlantic City.

"That's what I saw in the business. When he began to have pressure with debts, when the [Taj Mahal casino in Atlantic City] was underperforming, is when he began acting very erratically."

O'Donnell pointed to the mounting pressure on Trump with the Russia investigation by Special Counsel Robert Mueller and the scandal surrounding Trump's alleged affair with a pornographic film star.

"I think he likes the vision of himself being in control," O'Donnell said. "I doubt he realises the consequences of North Korea just like he didn't realise the consequences in business of walking in and firing someone at the Taj without thinking about it. It's Trump."

Critics warned that Trump was overseeing a massive consolidation of group-think within the West Wing, driving out top advisers who have challenged him on national security and economic decisions and elevating those who confirm his protectionist leanings - a signal, perhaps, to numerous cabinet members that they must fall in line or be the next to go.

National Economic Council Director Gary Cohn resigned in protest over the tariffs decision. Tillerson, who had crossed Trump on the Iran deal and was more critical of Russian misbehaviour than the White House has been, was summarily fired in a presidential tweet hours after returning from a week-long trip to Africa.

Attention is now focused on the fate of national security adviser H.R. McMaster, who has had a rocky relationship with the President and has battled an internal power struggle for months.

Eliot Cohen, who served as a State Department counsellor in the George W. Bush Administration, said Tillerson was the worst Secretary of State in recent memory. But Cohen, who led one of the two "never-Trump" letters signed by dozens of national security experts during the campaign, said Trump's intent to nominate CIA Director Mike Pompeo to replace him will lead to even less internal debate.

Tillerson had dismissed the idea of direct talks with North Korea just days before Trump announced a summit with Kim Jong Un. By contrast, Pompeo lavished praise on Trump's strategy with Pyongyang.

"We have a very similar thought process," Trump said of the CIA chief.

"This means conversations will be more of a 'never, never land' than they already are," Cohen said. "You will hear nothing faintly resembling candid disagreements."

The departures of Cohn and Tillerson, in particular, also represent a move by Trump toward his more nationalistic instincts. Both men came to the White House after successful careers as top executives at international corporations - Tillerson at ExxonMobil and Cohn at Goldman Sachs.

They defended such things as climate change treaties and trade deals - positions that led far right critics, such as former White House strategist Stephen Bannon, to deride them as "globalists" - and now that viewpoint will be far less represented in Trump's Administration.

Last week, Trump said he liked having divergent viewpoints within the White House. But at Cabinet meetings, Trump has allowed reporters in to witness a display of unusual obsequiousness. In December, for example, Vice-President Mike Pence commended Trump once every 12 seconds for three minutes.

"If you are going to work for the President, you fight it out, and if you lose you don't go behind the President's back and attack it, you defend the policy," said Steve Moore, an economic adviser to Trump during the 2016 campaign. "If you can't do that, you shouldn't have taken the job in the first place."

But there are signs that aides have fewer chances to fight for their positions.

Last week, Trump decided on the spot during a 45-minute meeting with South Korean officials in the Oval Office that he would accept an invitation from Kim to meet for talks - stunning senior aides, including Mattis and McMaster, who warned about moving too quickly.

Jon Wolfsthal, who served as senior director for arms control and nonproliferation at the National Security Council under former president Barack Obama, said most presidents would have convened an interagency meeting with the relevant federal agencies before making such a momentous decision.

"A president could hear from his Cabinet about whether it was worth the risk and, if it was worth the risk, how they would make the announcement, who to inform first," Wolfsthal said.

Trump asked his South Korean interlocutors to announce the news in the West Wing driveway as he hastily tried to reach the leaders of Japan and China. Tillerson, who was travelling in Africa, was represented at the Oval Office meeting by a deputy.

The following day, White House press secretary Sarah Huckabee Sanders sowed confusion by telling reporters that the meeting was contingent on Pyongyang taking active steps to denuclearise, before one of Sanders aides later clarified by saying there were no preconditions to the summit.

"The impression people are being given right now is that Trump feels he has been poorly served by his staff," Wolfsthal said. "Cabinet secretaries aren't doing job he wants. He is relying much more on himself."

Or people who reflect his own image. One of the top candidates to replace Cohn, Larry Kudlow, a conservative television commentator who served in the Reagan Administration, had previously spoken out against Trump's tariff plan. But Trump today said Kudlow "now has come around to believing in tariffs as a negotiating point."

Trump also met recently with former United Nations ambassador John Bolton, who is viewed as more hawkish on Iran than McMaster or Tillerson.

The turmoil has unsettled US allies and rivals across the globe.

"I think the Chinese are reeling from this presidency," said Bonnie Glaser, a China expert at the Centre for Strategic and International Studies.

She noted that Beijing has sought to develop ties to both Tillerson and Kushner, who has lost standing amid questions about his inability to gain a security clearance and financial debts tied to his family's real estate business.

"The Chinese ambassador has been going around quietly seeing very senior former officials and asking them who to talk to," Glaser said. "How can they influence this Administration? Every day is a new surprise for them."