Donald Trump Takes G.O.P. Mantle

CLEVELAND — Donald John Trump accepted the Republican presidential nomination on Thursday night with an unusually vehement appeal to Americans who feel that their country is spiraling out of control and yearn for a leader who will take aggressive, even extreme, actions to protect them.

Mr. Trump, 70, a New York real estate developer and reality television star who leveraged his fame and forceful persona to become the rare political outsider to lead the ticket of a major party, drew exuberant cheers from Republican convention delegates as he strode onto the stage of the Quicken Loans Arena and delivered a speech as fiery as his candidacy.

With dark imagery and an almost angry tone, Mr. Trump portrayed the United States as a diminished and even humiliated nation, and offered himself as an all-powerful savior who could resurrect the country’s standing in the eyes of both enemies and law-abiding Americans.

“Our convention occurs at a moment of crisis for our nation,” an ominous-sounding Mr. Trump said, standing against a backdrop of American flags. “The attacks on our police, and the terrorism in our cities, threaten our very way of life. Any politician who does not grasp this danger is not fit to lead our country.”

Mr. Trump nearly shouted the names of states where police officers had been killed recently, as the crowd erupted in applause, and returned repeatedly to the major theme of the speech: “Law and order,” he said four times, each time drawing out the syllables.

Evoking the tumult of the 1960s and the uncertainty that followed the Sept. 11 terrorist attacks, Mr. Trump made a sharp departure from the optimistic talk about American possibility that has characterized Republican presidential candidates since Ronald Reagan redefined the party over 30 years ago. In promoting his hard-line views on crime, immigration and hostile nations, Mr. Trump was wagering that voters would embrace his style of populism and his promises of safety if they feel even less secure by Election Day.

But his speech — the longest, at an hour and 15 minutes, since at least 1972 — had relatively little new to offer women, Hispanics, blacks and others who have been turned off by Mr. Trump’s incendiary brand of politics. He did sound like a different sort of Republican at times, though, making no mention of abortion — a core issue for many Republicans — and saying of his support among evangelical voters, “I’m not sure I totally deserve it.”

Mr. Trump also challenged Republican orthodoxy as he promised to end multilateral trade deals and limit American intervention in global crises. He denounced “15 years of wars in the Middle East” — a rebuke of his party’s last president, George W. Bush — and pledged to help union members, coal miners and other low-wage Americans who have historically supported Democrats.

“These are the forgotten men and women of our country,” said Mr. Trump, a billionaire with a mixed record of job creation and layoffs. “People who work hard but no longer have a voice — I am your voice.”

He even vowed “to do everything in my power to protect our L.G.B.T.Q. citizens from the violence and oppression of a hateful foreign ideology.’’ As the audience applauded, Mr. Trump made a deviation from his prepared text, observing: “I have to say, that as a Republican, it is so nice to hear you cheering for what I just said.”’

Facing a restive party on the final night of a convention that has been unusually turbulent and divided, Mr. Trump seemed to make headway in galvanizing and unifying at least those Republicans gathered in the hall. The nearly full arena was rapt as Mr. Trump spoke, and when he began discussing illegal immigration, a familiar chant quickly broke out in the arena: “Build the wall, build the wall!”

And when he vowed to tell the truth “plainly and honestly,” a delegate cried from the floor: “Bring it, Donald!”

Mr. Trump dwelled at length on illegal immigrants and lawless Americans, saying they are as dangerous for the nation’s security as the Islamic State and Syrian refugees. In doing so, Trump advisers said, he sought to win over undecided voters who are sickened by the recent violence against police officers and worried about safety yet are unsure if Mr. Trump has the temperament and abilities to be commander in chief.

“I have a message to every last person threatening the peace on our streets and the safety of our police: When I take the oath of office next year, I will restore law and order to our country.”

While nomination speeches are traditionally optimistic and personal, full of hope and revelations that cast candidates in the best possible light for voters, Mr. Trump sounded like a wartime president, using the word “threat” seven times and promising to “defeat the barbarians of ISIS.” He also recited homicide rates in American cities and the thousands of illegal immigrants with criminal records, promising to control violence at home and abroad.

“It is time to show the whole world that America is back — bigger, and better and stronger than ever before,” Mr. Trump said.

He was blistering about Hillary Clinton, his Democratic opponent, and her tenure as secretary of state, arguing that her diplomatic strategy in Syria, Iraq, Egypt, Libya and other countries had led to civil unrest and political chaos and rendered her unfit to be president.

“America is far less safe — and the world is far less stable — than when Obama made the decision to put Hillary Clinton in charge of America’s foreign policy,” Mr. Trump said.

Mr. Trump said Americans had “lived through one international humiliation after another” under President Obama: the Navy sailors “being forced to their knees” by Iranian captors in January; the destruction of the American consulate in Benghazi, Libya; and Mr. Obama’s decision not to defend his “red line” on Syria.

Mrs. Clinton shared the blame, too, he added.

“This is the legacy of Hillary Clinton: death, destruction, terrorism, and weakness,” Mr. Trump said.

In a bid to appeal to Democrats unhappy with their party’s embrace of Mrs. Clinton, he invoked the political message of her chief rival, Senator Bernie Sanders, and suggested that Mr. Sanders shared Republicans’ critique of her record.

Mr. Trump’s elder daughter, Ivanka, also sought to reach out to Democrats and moderates, extolling him as a champion of women in the workplace, and a leader who would “take on the bold and worthy fights, who will be unafraid to set lofty goals and relentless in his determination to achieve them.”

This week’s convention, which typically would have been choreographed carefully, was itself a departure from the norm. But if Mr. Trump injected drama and even spontaneity back into the formulaic gathering, he also tested the limits of improvisation over the last week.

The operatic quality of the first three days of the convention worried some Republicans. Presidential candidates have two major issues to deal with over the summer, their vice-presidential selection and their convention, and they felt he had bungled both. Mr. Trump chose his running mate haphazardly and then overshadowed the announcement of Gov. Mike Pence of Indiana by indulging in a rambling speech that revived questions about his seriousness.

The party staged a convention that reflected just how fractured it is. There were, to be sure, effective attacks on the character and record of Mrs. Clinton, whose unpopularity among modern presidential nominees is exceeded only by Mr. Trump’s. But some of the anti-Clinton language spilled into ugliness and catcalls. The party at times seemed unified only around a shared determination to imprison the former secretary of state.

But the speeches dedicated to promoting Mr. Trump and the party’s governing vision were hazy and at times collided with the candidate’s own beliefs. Many of the elected officials who spoke extolled a traditional conservative platform that bears little relation to the nationalist agenda on which Mr. Trump is basing his campaign.

For example, just hours before Mr. Pence, a committed internationalist, assured delegates and millions of voters that America would defend its allies, Mr. Trump gave an interview in which he balked at defending NATO countries, a policy that has been the cornerstone of the alliance for 70 years.

Even as Republicans prepared to leave Cleveland, they were still straining to come to terms with the views and personality of their newly minted nominee.

“I’m going to vote for Mike Pence,” said Gov. Gary Herbert of Utah, pausing for effect: “And Donald Trump comes along with the package.”

Candidates who are trailing — as Mr. Trump is, according to national polling averages — must maximize the bump they typically enjoy in the polls after their conventions. Mr. Trump may see his standing improve after he leaves Cleveland on Friday, even though he did not fully seize the opportunity he was afforded after Mrs. Clinton was upbraided by the F.B.I. director over her private email server.

In many ways, the convention’s formality was an awkward fit for Mr. Trump, who soared in the primaries by energizing voters at freewheeling rallies with his off-the-cuff and frequently entertaining remarks.

Instead, for Thursday night, he relied on a teleprompter and a speech heavy with familiar Republican themes like cutting taxes, creating jobs, and pushing for education reforms to give parents more choice in schools for their children.