“We will no longer accept politicians who are all talk and no action, constantly complaining but never doing anything about it,” he said. “The time for empty talk is over. Now arrives the hour of action. Do not allow anyone to tell you that it cannot be done.”

Mr. Trump’s view of the United States was strikingly grim for an Inaugural Address — a country where mothers and children are “trapped in poverty in our inner cities,” where “rusted-out factories” are “scattered like tombstones across the landscape” and where drugs and crime “have stolen too many lives.”

“This American carnage,” he declared, “stops right here and stops right now.”

He got started right away with rolling back the policies of his predecessor, former President Barack Obama, by issuing orders freezing new regulations from recent weeks and ordering agencies to “ease the burden” of the Affordable Care Act during the transition from repealing to replacing the law. More orders are planned for next week.

Wearing a dark suit and red tie and accompanied by his wife, Melania, in a powder-blue suit and matching gloves, Mr. Trump took the 35-word oath administered by Chief Justice John G. Roberts Jr. precisely at noon. Michael Richard Pence, a former governor and congressman from Indiana, was sworn in minutes before as vice president by Justice Clarence Thomas.