After he took the oath of office on the West Front of the Capitol, President Trump began his inaugural address saying "together we will determine the course of America and the world for many, many years to come."
He vowed to put "America first" and stand for everyone, including the forgotten men and women who "will never be ignored."
He added that the transferring of power from one party to another was not the only thing taking place. His message was "we are transferring power from Washington, D.C. And giving it back to you, the people."
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Campaign rival Hillary Clinton was present for the ceremony, sitting just a few seats away from Trump. She tweeted to her fans and followers, reassuring them she "will never stop believing in our country & its future."
I'm here today to honor our democracy & its enduring values. I will never stop believing in our country & its future. #Inauguration— Hillary Clinton (@HillaryClinton) January 20, 2017
Trump fans were at the nation's capital for the inaugural celebrations, many wearing red hats with his popular campaign slogan "Make America Great Again."
"I'm here for history," said Kevin Puchalski, a 24-year-old construction worker who drove from Philadelphia to attend the swearing-in. "This is the first president that I voted for that won." His big hope: Trump builds that promised wall on the U.S.-Mexican border. "Keep the illegals out," he said.
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Meantime, dozens of Democratic lawmakers were boycotting the ceremony on Capitol Hill. Trump faces a divided nation that is still reeling from the long and controversial presidential race.
Immediately after his and Vice President Mike Pence's swearing-in, Trump embraced members of his family and waved to the crowd on the National Mall.
The president started his inauguration day with a morning tweet to his country saying, "It all begins today!" and "THE MOVEMENT CONTINUES - THE WORK BEGINS!"
It all begins today! I will see you at 11:00 A.M. for the swearing-in. THE MOVEMENT CONTINUES - THE WORK BEGINS!— Donald J. Trump (@realDonaldTrump) January 20, 2017
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He then attended church with his family and met former president Barack Obama and former first lady Michelle Obama for tea at the White House. The Trumps and the Obamas then traveled together for the swearing-in ceremony.
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Protesters came out early, some trying to block inaugural visitors from passing through security checkpoints, some wearing orange jumpsuits with black hoods over their faces.
Eleanor Goldfield, who helped organize the Disrupt J20 protest, said the message is they will not be silent during Trump's presidency.
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Meantime at the White House, moving trucks were on standby for the new first family, while the former was set to head out.
Obama also took to Twitter on his last hours as president, thanking the public for making him a "a better leader and a better man."
It's been the honor of my life to serve you. You made me a better leader and a better man.— President Obama (@POTUS) January 20, 2017
I'm still asking you to believe - not in my ability to bring about change, but in yours. I believe in change because I believe in you.— President Obama (@POTUS) January 20, 2017
He continued with follow-up tweets, making a promise to the people he "will be right there with you as a citizen."
I won't stop; I'll be right there with you as a citizen, inspired by your voices of truth and justice, good humor, and love.— President Obama (@POTUS) January 20, 2017
After the inauguration ceremony, the Trumps escorted the Obamas to the presidential plane, but it won't be referred to as Air Force One because that designation only applies when the current president is on board.
Following plans to address a farewell gathering of staff at Joint Base Andrews, Obama and his family plan to travel to Palm Springs.
It's unclear how long the Obamas will be in Palm Springs, but they aren't expected to host any public events while in California.
The Obamas have rented a home in Washington and intend to live there as private citizens until Sasha finishes high school.
The Associated Press contributed to this report.