US President Donald Trump's surprising rise to the presidency four years ago upset many assumptions and taboos, but the 74-year-old former real estate mogul and reality television star is now fighting for his political life.

His come-from-behind win in 2016, by claiming outsider status and promising to bring a businessman's acumen for dealmaking to the White House, shocked much of the US political ecosystem.

His governing style continues to be seen as aggressive, brash and combative. But it has been hard for him to make the most of the opinion polls leading up to the elections, where he has been steadily trailing opponent Joe Biden this year.

Whatever claims he was able to make about the economy under his watch including historically low unemployment rates - have been battered by the coronavirus, although the economy did show a fast expansion in the third quarter.

His style of governance has increasingly run into the problem of effectiveness. Healthcare remains largely unchanged and trade deals have yet to be significantly revamped, as he pledged. He's brought attention to relations with China, but no resolution.

Running on "make America great again" for a second time has been a harder task. He has touted a record of appointing conservative judges, protecting gun ownership rights and being pro-business.

Trump was born June 14, 1946, the fourth of five children of Frederick Trump, a real estate magnate who bequeathed a small New York empire to his family.

At age 13, Trump's parents sent him to a military academy. The future president went on to study at Fordham University and then the University of Pennsylvania's prestigious Wharton School of Business.

After graduating from Wharton, he joined his father's business and in 1974 became its president and renamed it the Trump Organization.

Investments in hotels, casinos, golf courses and luxury apartments followed.

Trump dabbled in entertainment and media investments, including the Miss USA and Miss Universe beauty pageants. His roles in the TV reality show "The Apprentice" and "The Celebrity Apprentice" followed. When it was time to dismiss a contestant, he told them curtly, "You're fired."

Trump dipped into politics from time to time but never made a serious effort. Some of his runs appeared designed just to boost his profile and add to his celebrity.

However, he seemed galvanized under former president Barack Obama, becoming a right-wing populist and famously questioning whether the US' first black president was actually born in the country, an allegation with racist undertones.

His 2016 campaign was rife with such jabs, saying many Mexican immigrants were rapists and murderers and promising to ban Muslims from entering the country.

He also faced allegations of sexual harassment and never released his tax returns, a long-time tradition in the US for presidential candidates.

It was, however, the alleged links to Russian election interference that came to haunt his presidency, leading to numerous inquiries that took up his time and energy and led to endless battles.

Trump's hatred of what he described as the "deep state" and the "fake news media" only seemed to grow as his problems mounted, including legal investigations that emerged over his real estate businesses.

He was impeached, though not convicted, over his Ukraine links.
The catchphrase "you're fired" also appeared to follow him later in government, as his cabinet and top staff saw high turnover, adding to a sense of chaos at times at the White House.

The pandemic this year has hit the US particularly hard and the White House was repeatedly blamed for a poor response and a lack of empathy.

In office, he has at times appeared to wink at far-right groups and white nationalists. Trump failed to settle on a message during the Black Lives Matter demonstrations that would broaden his appeal, instead demanding simply law and order.