WASHINGTON - Donald Trump took power as the 45th president of the United States on Friday and pledged to pursue "America First" policies in an inaugural address that was a populist, anti-Washington rallying cry.
Sketching a bleak vision of a country he said was ravaged by rusted-out factories, crime, gangs and drugs, Trump indirectly blamed his predecessors in the White House for policies that helped the establishment at the expense of struggling families.
"From this moment on, it's going to be America First," the Republican told hundreds of thousands of people gathered on the grounds of the National Mall after taking the oath of office on the West Front of the U.S. Capitol.
Four past U.S. presidents, three Democrats and a Republican, sat nearby. Scattered street protests erupted against Trump elsewhere in Washington.
"Every decision on trade, on taxes, on immigration, on foreign affairs, will be made to benefit American workers and American families," Trump said, describing the country's social and economic ills as "American carnage."
Trump, 70, takes over a country divided after a savage election campaign. A wealthy New York businessman and former reality TV star, he will set the country on a new, uncertain path at home and abroad.
Trump's inaugural address revisited the themes of the campaign rally speeches that carried him to an improbable victory on Nov. 8 over Democrat Hillary Clinton, who attended the ceremony with her husband, former President Bill Clinton.
Under pressure to unite the country after the bitterly fought campaign, Trump said that through allegiance to the United States, "we will rediscover our loyalty to each other" and called for a "new national pride" that would help heal divisions.
Abroad, Trump signaled the possibility of a more aggressive approach to Islamic State militants than his immediate predecessor, Democrat Barack Obama.
"We will reinforce old alliances and form new ones, and united the civilized world against radical Islamic terrorism, which we will eradicate completely from the face of the earth," he said.
After repeating the 35-word oath of office, Trump stretched his arms wide and hugged his wife, Melania, and other members of his family. Ceremonial cannon blasts fired.
The transition from a Democratic president to a Republican took place before a crowd of former presidents, dignitaries and hundreds of thousands of people on the grounds of the National Mall. The crowd stretched westward on a cool day of occasional light rain.
Away from the Capitol, masked activists ran through the streets smashing windows with hammers at a McDonald's restaurant, a Starbucks coffee shop and a steakhouse several blocks from the White House.
They carried black anarchist flags and signs that said, "Join the resistance, fight back now." Police used pepper spray and chased them down a major avenue.
In another location not far from the White House, protesters also scuffled with police, at one point throwing aluminum chairs at them at outdoor café.
Former presidents George W. Bush and Jimmy Carter were present at the inauguration with their wives. Bush's father, former President George H.W. Bush, 92, was in Houston recovering from pneumonia.
Trump and his vice president, Mike Pence, began the day with a prayer service at St. John's Episcopal Church near the White House.
Trump took office with work to do to bolster his image.
An ABC News/Washington Post poll this week found only 40 percent of Americans viewed him favorably, the lowest rating for an incoming president since Democrat Carter in 1977, and the same percentage approved of how he has handled the transition.
During a testy transition period since his election win, Trump has repeatedly engaged in Twitter attacks against his critics, so much so that one fellow Republican, Senator John McCain, told CNN that Trump seemed to want to "engage with every windmill that he can find."
His ascension to the White House, while welcomed by Republicans tired of Obama's eight years in office, raises a host of questions for the United States.
Trump campaigned on a pledge to take the country on a more isolationist, protectionist path and has vowed to impose a 35 percent tariff on goods on imports from U.S. companies that went abroad.
His desire for warmer ties with Russian President Vladimir Putin and threats to cut funding for NATO nations has allies from Britain to the Baltics worried that the traditional U.S. security umbrella will be diminished.
In the Middle East, Trump has said he wants to move the U.S. Embassy in Israel from Tel Aviv to Jerusalem, at the risk of angering Arabs and stirring international concern. He has yet to sketch out how he plans to carry out a campaign pledge to "knock the hell out of" Islamic State.
More than 60 Democratic lawmakers stayed away from the proceedings to protest Trump, spurred on after he derided U.S. Representative John Lewis of Georgia, a hero of the civil rights movement, for calling him an illegitimate president.
Many demonstrators are to participate in a "Women's March on Washington" on Saturday. Protests are also planned in other cities in the United States and abroad.
Trump's to-do list has given Republicans hope that, since they also control the U.S. Congress, they can quickly repeal and replace Obama's signature healthcare law, approve sweeping tax reform and roll back many federal regulations they say are stifling the U.S. economy.
"He's going to inject a shock to the system here almost immediately," Trump senior adviser Kellyanne Conway told Fox News.
Democrats, in search of firm political footing after the unexpected defeat of Hillary Clinton, are planning to fight him at every turn. They deeply oppose Trump's anti-immigrant rhetoric from the campaign trail and plans to build a wall along the southern U.S. border with Mexico.
Trump's critics have been emboldened to attack his legitimacy because his win came in the Electoral College, which gives smaller states more clout in the outcome. He lost the popular vote to Clinton by about 2.9 million.
Trump's critics also point to the conclusion of U.S. intelligence agencies that Russia used hacking and other methods during the campaign to try to tilt the election in the Republican's favor. Trump has acknowledged the finding - denied by Moscow - that Russia was behind the hacking but said it did not affect the outcome of the election.