Donald John Trump completed an extraordinary return to power on Monday as he was sworn in as the 47th president of the United States and promised an immediate blitz of actions to begin drastically changing the course of the country and usher in a new “golden age of America.”

In a triumph of the man and his movement, Mr. Trump took the oath of office during a ceremony in the Capitol four years after he was evicted by voters, reinvigorated for another term aimed at remaking America in his vision. He wasted no time outlining an ambitious program of often divisive policies to “reclaim our Republic” and purge its enemies and his own.

“My recent election is a mandate to completely and totally reverse a horrible betrayal and all of these many betrayals that have taken place, and to give the people back their faith, their wealth, their democracy, and indeed, their freedom,” Mr. Trump said during a 29-minute Inaugural Address as former President Joseph R. Biden Jr. looked on. “From this moment on, America’s decline is over.”

Feeling vindicated by voters after impeachments, indictments and conviction on 34 felony counts, Mr. Trump claimed a personal mandate as well as a political one. “Many people thought it was impossible for me to stage such a historic political comeback,” he said. “But as you see today, here I am. The American people have spoken.”

Indeed, he saw divine intervention in his restoration to the White House, citing his close call during an assassination attempt this summer. “I felt then, and believe even more so now, that my life was saved for a reason,” he said. “I was saved by God to make America great again.”