He has promised to "Make America Great Again", but rain threatened to turn Donald Trump's big moment into a washout.
An estimated 800,000 people crushed into the centre of Washington, DC for the 58th US Presidential inauguration, sheltering from the drizzle under raincoats and ponchos.
A steel ring of security encircled the centre of the city, with roads blocked off and police on every corner.
But tight security and grey skies over the famous white dome of the Capitol building failed to dampen the enthusiasm of Trump's supporters.
"Trump is going to 'Make America Great Again' and undo the wreckage of Obama," said Joe Smith, 69, from Tampa, Florida.
"I believe that the enemies of this country have been allowed to fester for too long, and Donald Trump is going to change that," said Nick Graham, 20, from Pasadena, Maryland.
Crammed in next to Trump's supporters, Clinton voters looked on solemnly while protestors chanted.
"We came today to show that we are not giving our consent for this presidency," said Erica West, 21, from Arlington, Virginia.
"Donald Trump stands for hatred, racism and misogyny. That's against everything that I stand for as a citizen of this country," said Kevin Cannell, 31, from New Orleans.
At a Black Lives Matter demonstration in a small park just off the National Mall, impromptu arguments broke out between protesters and passing Trump supporters in "Make America Great Again" hats.
As the hour of the inauguration ceremony approached, demonstrators linked arms to block the route to the viewing area.
They chanted "this checkpoint is closed, go home" as police tried to break up the line to allow spectators through.
"Criminal-in-Chief," read one protestor's placard.
"The power of the people is stronger than the people in power," proclaimed another.
Eight years after Barack Obama swept into power riding a message of hope, Donald Trump is taking charge of a divided America.
The wounds from a bitter election were still fresh for many on his inauguration day.
But the Trump administration say they can bring the country together again.
"We're going to unify our country, and our phrase - you all know it - 'Make America Great Again!'. But we're going to make America great for all of our people," said Trump at a welcome celebration at the Lincoln Memorial on the eve of his inauguration.
But just hours before the handover of power, a Fox News survey put Trump's approval ratings at 37 per cent.
Fifty-four per cent say they do not approve of the country's new president.
With historically low ratings for a first-time president, Trump's first 100 days could define his time in office.
The fractious atmosphere at his inauguration shows that the fervour of his supporters is matched by the anger of his opponents.