LIVE VIDEO: ABC News Inauguration Coverage
The billionaire businessman and former reality television star has pledged an era of profound change, energizing his supporters with promises to wipe away predecessor Barack Obama's signature achievements and to restore America to a lost position of strength. But Trump's call for restrictive immigration measures and his caustic campaign rhetoric about women and minorities have infuriated other millions of Americans. He assumes office as one of the most unpopular incoming presidents in modern history.
FULL VIDEO: President Trump addresses nation after being sworn in
The pomp and pageantry of the inaugural celebrations were also shadowed by questions about Trump's ties to Russia, which U.S. intelligence agencies have determined worked to tip the 2016 election to help the Republican win.
Trump's inauguration drew crowds to the nation's capital to witness the history. It repelled others. More than 60 House Democrats refused to attend his swearing in ceremony in the shadow of the Capitol dome. One Democrat who did sit among the dignitaries was Hillary Clinton, Trump's vanquished campaign rival who was widely expected by both parties to be the one taking the oath of office.
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Instead, it was Trump placing his hand on two Bibles, one used by his family and another used for President Abraham Lincoln's inauguration. At 70, Trump is the oldest person to be sworn in as president, marking a generational step backward after two terms for Obama, one of the youngest presidents to serve as commander in chief.
The District of Columbia police chief said 217 people were arrested and charged with rioting and six officers suffered minor injuries during demonstrations against Mr. Trump.
Meanwhile, protesters in downtown Washington linked arms, facing off from the police line and chanting, "No Trump, No KKK, No Fascist USA."
Metropolitan police have deployed streams of pepper spray against demonstrators marching along the streets of the nation's capital - a disgruntled parallel to the ongoing inaugural parade.
Trump takes charge of an economy that has recovered from the Great Recession but has nonetheless left millions of Americans feeling left behind. The nation's longest war is still being waged in Afghanistan and U.S. troops are battling the Islamic State in Iraq and Syria. The American health care system was expanded to reach millions more Americans during Obama's tenure, but at considerable financial costs. Trump has vowed to dismantle and rebuild it.
Trump faces such challenges as the first president to take office without ever having held a political position or served in the military. He has stacked his Cabinet with established Washington figures and wealthy business leaders. Though his team's conservative bent has been cheered by many Republicans, the overwhelmingly white and male Cabinet has been criticized for a lack of diversity.
Officials expected hundreds of thousands of people to flock to the National Mall to witness the inauguration of the 45th president, though early crowds appeared smaller than past celebrations. Demonstrations unfolded at various security checkpoints near the Capitol as police in riot gear helped ticket-holders get through to the ceremony.
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In a show of solidarity, all of the living American presidents attended the swearing-in ceremony, except for 92-year-old George H.W. Bush, who was hospitalized this week with pneumonia. His wife, Barbara, was also admitted to the hospital after falling ill.
While Trump came to power bucking convention, he wrapped himself in the traditions that accompany the peaceful transfer of power. Following a morning church service with his family, Trump and his wife, Melania, had tea at the White House with Obama and outgoing first lady Michelle Obama.
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The two couples greeted each other with handshakes and hugs, and Mrs. Trump presented Mrs. Obama with a gift. Following their private gathering in the executive mansion, the Trumps and Obamas traveled together to the Capitol for the swearing in ceremony.
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