Donald John Trump was sworn in Friday as the nation’s 45th president and delivered a fiery nationalist manifesto that promised a populist restoration by stripping power from Washington’s elites and ending an era of “American carnage.”

Framing his ascension as transformational and global in its impact, Trump delivered a dark inaugural address in which he pledged fealty to all Americans. But he made little overt attempt to soothe a nation still wounded from arguably the ­ugliest election season of modern times and signaled that he intends to govern as if waging a permanent political campaign.

As Trump addressed hundreds of thousands of supporters from the West Front of the Capitol — a crowd plainly more sparse and subdued than the record one for Barack Obama’s historic inauguration eight years ago — scores of violent protesters clashed with police in the streets of downtown Washington.

Trump reprised the central ­arguments of his candidacy and harshly condemned the condition of the country he now commands. He said communities had fallen into disrepair with rampant crime, chronic poverty, broken schools, stolen wealth and “rusted-out factories scattered like tombstones.”

“This American carnage stops right here and stops right now,” Trump declared in his 16-minute address.

A limousine burns from protesters on the streets of Washington on the day of President Trump’s inauguration. (Matt McClain/The Washington Post)

“We assembled here today are issuing a new decree to be heard in every city, in every foreign capital and in every hall of power,” he added. “From this day forward, a new vision will govern our land. From this day forward, it’s going to be only America first. America first.”

Trump immediately settled into the job, beginning a series of executive actions designed to systematically tear down Obama’s legacy. He signed one executive order pertaining to the Affordable Care Act that White House press secretary Sean Spicer said would “ease the burden of Obamacare as we transition to repeal and replace.” Separately, White House Chief of Staff Reince Priebus planned to issue a memorandum to all federal departments and agencies ordering an immediate freeze on regulations.

Trump signed the health-care ­order while seated at the Resolute Desk of the Oval Office, which had been redecorated with gold curtains (a change from Obama’s crimson drapes). Busts of President Theodore Roosevelt and former British prime minister Winston Churchill were added to be displayed along with one of civil rights icon Martin Luther King Jr.

The day of pageantry and ritual — orchestrated both to celebrate the installation of a new commander in chief and to symbolize a peaceful transfer of power — began with a church service and included a military review, a triumphant ­parade down Pennsylvania Avenue and evening balls.

A tuxedo-clad Trump and wife Melania, who wore an off-the-shoulder white gown, performed their first dance to a cover of Frank Sinatra’s “My Way,” with the president mouthing the lyrics.

[‘I do solemnly swear…’: The 35 most momentous words Donald Trump will say at his inauguration]

The proceedings showcased the paradoxes of Trump. His inaugural speech, delivered in a light rain, presented a scathing indictment of the very lawmakers and former presidents who sat behind him on the dais. The president charged the ­entrenched powers in both political parties with exploiting “the forgotten men and women of our country.”

(Sarah Parnass/The Washington Post)

“The time for empty talk is over,” Trump said. “Now arrives the hour of action.”

Yet moments later, retreating ­inside the Capitol for a signing ceremony of his first executive actions, the president was chummy with the congressional leaders from both parties who embody the established order he had vowed to destroy.

Trump made no mention in his address of his Democratic opponent, former secretary of state Hillary Clinton, who received nearly 3 million more votes than Trump yet lost to him in the electoral college.

But later at a luncheon in the Capitol’s Statuary Hall, Trump said he was “very, very honored” that Clinton — whom he derided during the campaign as “Crooked Hillary” — had attended the inauguration with former president Bill Clinton and asked the other dignitaries in the room to applaud the couple.

In yet another paradox, Trump said his presidency would be governed by two simple rules: “Buy American and hire American.” In building his sprawling business empire, however, Trump relied heavily on imports and immigrant labor.

And as Trump promised to return power to “struggling families,” two of his wealthiest benefactors — casino mogul Sheldon Adelson and wife Miriam — were among the day’s guests of honor, scoring prime aisle seats behind Trump on the dais. [A fierce will to win pushed Donald Trump to the top]

Trump, who sees his election as part of a global movement that includes Britain’s decision to leave the European Union, wanted his speech to resonate beyond the country’s borders. He said at the outset that he was addressing “fellow Americans and people of the world.”

Trump echoed the nationalist mantra of President Andrew Jackson, saying he would focus entirely on rebuilding America and promoting its interests.

“Every decision on trade, on taxes, on immigration, on foreign affairs will be made to benefit American workers and American families,” Trump said. “We must protect our borders from the ravages of other countries making our products, stealing our companies and destroying our jobs.”

At 70, Trump became the oldest president ever sworn into office for the first time and one of the wealthiest in history. His far-reaching business holdings, which he said he has placed in a trust to be administered by his two adult sons, have prompted questions about how he will separate his personal financial interests from those of the country.

Trump, who wore a dark suit and his signature red tie, used a family Bible as well as President Abraham Lincoln’s Bible to take the oath of office, which was administered by Chief Justice John G. Roberts Jr.

Trump’s wife, Melania, who wore a powder-blue cashmere dress, their son Barron, 10, and the president’s four adult children from his two previous marriages looked on, as did Vice President Pence and his family.

The ceremony was much in keeping with tradition. It featured prayers from an array of religious leaders and music by the U.S. Marine Band and the Mormon Tabernacle Choir.

But the crowd that spilled onto the Mall gave the proceedings a distinctly Trumpian flavor. There were jeers when Senate Minority Leader Charles E. Schumer (D-N.Y.) was called upon to speak, and when Trump stepped forward to take the oath, people chanted, “Trump! Trump! Trump!”

The crowd, however enthusiastic, was visibly smaller than the turnout for Obama’s inauguration in 2009, when Washington was infused with a sense of hope.

Elsewhere in the city Friday, there were loud congregations of protesters holding anti-Trump signs. Some groups of black-clad anarchists roamed streets downtown smashing windows of businesses and cars, lighting a bonfire and hurling bricks and rocks at police, who responded with loud “flash-bang” grenades and streams of pepper spray.

Attendance was expected to be robust Saturday at the Women’s March on Washington, a display of opposition to Trump. City officials said that four times as many requests were made for parking permits for buses that day than on the day of Trump’s inauguration.

All but one living former president attended Trump’s swearing-in: George H.W. Bush watched the proceedings from a hospital in Houston, where he is recovering from a respiratory problem stemming from pneumonia.

Though the Democratic Party’s congressional leaders stood on the dais, more than 60 Democratic House members boycotted the inauguration.

Trump engaged warmly with his predecessor. Before the inauguration ceremony, President Obama and first lady Michelle Obama welcomed the Trumps for tea at the South Portico of the White House. Melania Trump presented Michelle Obama a gift — a box wrapped in the distinctive light blue of high-end jeweler Tiffany & Co. She seemed briefly perplexed about what to do with it, with the outgoing president looking in vain for someone to hold the box while the two couples posed for photographs.

Later, the 44th and 45th presidents exchanged pleasantries at the Capitol. Following the ceremony, the Trumps bade farewell to the Obamas, who lifted from the grounds in a Marine helicopter headed toward Joint Base Andrews.

There, Obama delivered brief remarks to a few hundred staff members and supporters before departing on his last flight aboard the aircraft otherwise known as Air Force One to Palm Springs, Calif., where he will vacation before settling into his new home in the Kalorama neighborhood of Washington.

Obama said he hoped his progressive movement would not be extinguished with Friday’s transfer of power. “This is not a period,” he said. “This is a comma in the continuing story of building America.”

Trump began dismantling Obama’s record, starting with reversing a recent mortgage insurance premium cut that had been projected to save some homeowners hundreds of dollars a year. Democrats denounced the action.

“President Trump, with the flick of a pen, ended that new policy, making it harder for Americans of modest means to obtain their piece of the rock, the American Dream — home ownership,” Schumer said on the Senate floor. “It only took an hour for those populist words delivered on the steps of the Capitol to ring hollow.”

[Moments after taking the oath, President Trump transforms White House website]

In his address, Trump was plain-spoken and direct, a deliberate contrast to the poetic oratory of his predecessor. Four years ago, Obama delivered a soaring ode to modern liberalism, from climate change to social transformation. In advocating for same-sex marriage, he became the first president to utter the word “gay” in an inaugural address.

Trump spoke of none of those issues, even though they have animated the Republican Party’s evangelical Christian base. He focused almost entirely on the economic anxieties of working people who feel dislocated and adrift.

“We’ve made other countries rich, while the wealth, strength and confidence of our country has dissipated over the horizon,” Trump said. “One by one, the factories shuttered and left our shores, with not even a thought about the millions and millions of American workers that were left behind. The wealth of our middle class has been ripped from their homes and then redistributed all across the world.

“But that is the past. And now, we are looking only to the future.”

Stephen K. Bannon, Trump’s White House chief strategist, who helped him craft the speech, said it was designed with Jackson in mind.

“It was an unvarnished declaration of the basic principles of his populist, and kind of nationalist, movement,” Bannon said. “I don’t think we’ve had a speech like that since Andrew Jackson came to the White House. But you could see it was very Jacksonian. It’s got a deep, deep root of patriotism there.”

Indeed, Trump sought to appeal to people’s patriotism to bridge the divide that lingers after the bruising campaign.

“When you open your heart to patriotism, there is no room for prejudice,” Trump said, adding: “It’s time to remember that old wisdom our soldiers will never forget, that whether we are black or brown or white, we all bleed the same red blood of patriots.”

Robert Costa, Paul Kane and Ashley Parker contributed to this report.