National Security Adviser Michael Flynn
However, some experts believed that Flynn's resignation was pushed by the US establishment or other people on Trump's team who disliked the retired lieutenant general. The main argument for such speculation was the fact that the never-before-used 1799 Logan Act, which criminalizes negotiation by unauthorized persons with foreign governments having a dispute with the United States, was invoked to sack him.
Chief strategist Steve Bannon
However, Bannon, the controversial advocate of immigration restrictions and radical economic policy changes, reportedly had a strained relationship with Trump's son-in-law and senior adviser, Jared Kushner, along with Gary Cohn, the director of the president's National Economic Council, and National Security Adviser HR McMaster. According to media reports, the president grew weary of Bannon's constant information leaks to alternative media and his taking undue credit for the president's successes. After The Donald came under fire for blaming "many sides" for violence during the Unite the Right rally in Charlottesville, Virginia, in August 2017, White House Press Secretary Sarah Huckabee Sanders announced August 18 that Bannon and the White House "mutually agreed" to spend some time apart.
Shortly after his resignation, Bannon was quoted in a new book as describing a meeting between Donald Trump, Jr. and Russian lawyer Natalia Veselnitskaya as "treasonous." Trump disavowed Bannon by saying "Steve Bannon has nothing to do with me or my presidency. When he was fired, he not only lost his job, he lost his mind." Shortly after, Bannon was cut loose by Breitbart's major investor and had to step down as a head of Breitbart as well.
National Security Adviser HR McMaster
In reality, though, the president and the general never really personally "gelled," in the words of the Washington Post. According to CNN, Trump had referred to the US Army lt. general's briefings as "gruff and condescending" and described the general himself as "aggressive" and prone to lectures. The two disagreed on the Iranian nuclear deal, with McMaster advocating for the 2015 Joint Comprehensive Plan of Action though Trump throughout his campaign called for tearing it up.
Apparently, the boiling point came after McMaster said during a forum in Germany in March 2018 it was "incontrovertible" that Russians had meddled in the 2016 presidential election.
"General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only collusion was between Russia and Crooked H[illary Clinton], the DNC and the Dems," a Trump tweet on February 18 read. March 22, after one year in office, McMaster was shown the door.
General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems. Remember the Dirty Dossier, Uranium, Speeches, Emails and the Podesta Company!— Donald J. Trump (@realDonaldTrump) 18 февраля 2018 г.
Secretary of State Rex Tillerson
The two publicly disagreed on a number of issues. Tillerson criticized Trump's decision to pull out of the Paris climate accord (a move heavily advocated by Steve Bannon). "I was free to express my views. I took a counter view to the decision that was made," Tillerson said in June 2017, confirming the rumors.
Trump also famously mocked Tillerson on Twitter for "wasting his time trying to negotiate with Little Rocket Man," referring to North Korea's leader, Kim Jong Un.
Tillerson also expressed his doubts, to say the least, about Trump's declared intention to end the war in Afghanistan with a complete US victory. "You will not win a battlefield victory. We may not win one, but neither will you," Tillerson said in August 2017, addressing the Taliban."So at some point, we have to come to the negotiating table and find a way to bring this to an end."
Tillerson also supported the position that Russia meddled with the US presidential elections that brought his boss into power. At the G20 summit in Hamburg, Germany, in July 2017, Tillerson told an associate he was "stunned" by the way Trump had approached Russian President Vladimir Putin on the issue. According to NY Times, Trump started his meeting with Putin by saying, "I'm going to get this out of the way: Did you do this?" According to Russian Foreign Minister Sergei Lavrov, Trump accepted firm assertions from Putin that the meddling allegations were false.
Let's also not forget that famous time the US top diplomat called the US president a "f*cking moron" before a group of top US national security officials. According to an NBC News report, the remark came after Trump said he wanted a wider nuclear arsenal, despite the decades-long trend of bilateral nuclear arsenal reduction by both Russia and the United States.
In October 2017, the New York Times called Tillerson an "isolated leader" of a "demoralized diplomatic corps." By December, the media was already saying Tillerson was "on his way out the door."
On March 13, 2018, Trump announced Tillerson was fired via Twitter, and that was how the now-ex state secretary discovered the news, reportedly by surfing Twitter while sitting on the toilet.
Economic Adviser Gary Cohn
Oddly enough, Cohn stood right behind Trump when the president made a speech blaming "both sides" for the deadly toll taken at the white supremacist Unite the Right rally in August 2017, during which a counter-protester was killed. Cohn caught his own share of blame for supporting the message.
Trump and Cohn clashed directly when Trump proposed imposing import tariffs on steel and aluminum. According to Politico, Cohn was "very passionate about" the metal tariff issue. Despite his reasoning and an attempt to organize a meeting between the president and the end users of steel and aluminum, Trump cancelled the meeting and imposed a 25 percent flat tax on steel imports and a 10 percent aluminum import tax.
Apparently, Cohn took the dispute personally, and on March 6, he announced his resignation.
"It has been an honor to serve my country and enact pro-growth economic policies to benefit the American people," the adviser said in a resignation statement.