Delivered on the steps of the Capitol, Trump's grim-toned inauguration speech depicted America as an economic basket case overrun by crime, street gangs and other blight, and attacked the politicians standing by him on the podium as pampered opportunists who prospered in government while everyday people missed out. Trump pledged to stop "this American carnage."
The very next day, a visibly nervous White House spokesman Sean Spicer appeared before reporters and insisted — against all evidence from aerial photos — that turnout on the National Mall had been greater than when Barack Obama was sworn in for his first term in 2008 and biased news outlets had it all wrong. The Trump presidency was one day old and already mired in controversy over its treatment of facts.
Out of the blue, on January 27, Trump signed an executive order imposing a 90-day ban on arrivals of people from seven Muslim majority countries and a 120-day ban on all refugee arrivals.
Chaos immediately broke out at US airports, with some travellers being detained upon arrival and security officials unsure how to implement the travel ban. Nationwide, Americans staged protests against a measure widely criticised as discriminating against Muslims. Trump said the order was designed to keep terrorists out of the United States.
The ban was quickly blocked in court, as was a modified version issued in March that removed Iraq from the list of targeted countries. The third iteration of the ban, which added citizens of North Korea and some Venezuelan government officials, was supposed to come into effect in mid-October. But again the courts stepped in to block it. Refugee admissions are to resume, except for people from 11 "high-risk" countries, most of which are Muslim majority.
In one of the most momentous and criticized moves of his presidency, Trump abruptly fired FBI director James Comey on May 9, sacking the man leading a probe into whether the Trump campaign colluded with Russia in an effort to defeat Hillary Clinton in the November election.
Trump first claimed that he was displeased with how Comey handled a probe into Clinton's use of a private email server as secretary of state under then president Barack Obama. But he later acknowledged publicly he had the Russia probe in mind when he fired Comey.
In the end, Trump's move backfired. The sacking led to the Justice Department's appointing of a more powerful, independent counsel, Robert Mueller, to head the investigation into Russian election meddling, which Trump routinely dismisses as "fake news."
On October 30, the Mueller-led probe yielded its first indictments: against former campaign manager Paul Manafort and a one-time business partner for money laundering, conspiracy and other alleged crimes, and, ominously, a little known ex-campaign adviser who confessed to talking to senior campaign officials about arrangements for meeting with Russian officials.
Trump announced on June 1 that he was pulling the United States out of the Paris climate change accord, dismissing appeals from environmental groups, foreign leaders, industry and even his own daughter Ivanka that he stick with the 195-nation accord to fight global warming.
Trump said the accord was bad for the US economy and American workers and gave other countries an unfair advantage, framing the decision as part of his America First campaign.
"I was elected to represent the citizens of Pittsburgh, not Paris," Trump declared. "We're getting out," he said. "And we will start to renegotiate and we'll see if there's a better deal. If we can, great. If we can't, that's fine."
On the campaign trail and once in office, Trump hammered away with a pledge to scrap the signature health care reform law enacted by Obama. It provided coverage for millions in a country with no universal health care system. Trump called it a disaster, citing dramatic rises in insurance premiums, among other problems.
But Trump quickly learned that campaign talk is one thing and getting something through the thicket of the US Congress is another, as his Republican Party failed to unite behind first one and then several other plans to scrap Obamacare, or at least change it.
In the most dramatic of these setbacks, in late July Senator John McCain, a strident Trump critic, flew back to Washington from his native Arizona after being diagnosed with brain cancer and in a wee hours of the morning Senate vote signaled with a thumbs-down sign that he would not back the Republican repeal-and-replace attempt.
People come and people go from the Trump White House, but no tenure was as turbulent as that of Anthony Scaramucci — whose July appointment as communications director led Sean Spicer, Trump's spokesman and for many the face of the administration, to resign in protest.
The brash, fast talking New York financier lasted just 10, headspinning days during which he stunned the world with an expletive-filled rant about fellow White House officials.
When a new, no-nonsense chief of staff, retired Marine general John Kelly, took over and set about putting order to a chaotic operation, Scaramucci — known as "the Mooch" — was toast and out the door.
In his maiden speech to the UN General Assembly, Trump boasted of America's military strength, signalled he was ready to rip up the nuclear accord with the "murderous regime" in Tehran, and vowed to destroy North Korea if its nuclear-armed regime threatened America or its allies.
Belittling Kim Yong-Un as a "Rocket Man" on a "suicide mission," Trump's address — one observer called it a "42-minute tweetstorm" — sent a shockwave around the world, and fuelled an escalating war of words with the North Korean leader.
But beyond the bellicose style, Trump showed glimmers of a doctrine that could transform America's place in the world, making it clear he wants to turn the clock back on half a century's growth of global rules and institutions and return to the primacy of the nation state.