A photo with Ronald Reagan, a framed "Playboy" cover and a view overlooking Central Park: Republican presidential candidate Donald Trump gives The Washington Post a tour of his office on the 26th floor of Trump Tower in New York. (Dan Balz/The Washington Post)

After a summer of dominating the Republican presidential campaign, Donald Trump is moving into a new and un­certain phase that the billionaire businessman acknowledges will be more challenging than any project he has ever undertaken — even as he views the nomination as now within his reach.

In an hour-long interview with The Washington Post at his 26th-floor office in Trump Tower, the Republican front-runner ruminated on the many obstacles ahead. Sitting at a desk piled high with magazine covers bearing his image and strewn with polls and other testaments to his early success, Trump said he is far from satisfied with what he has accomplished to date.

“If you don’t win, what have I done? I’ve wasted time,” he said. “I want to make America great again, and you can’t do that if you come in a close second.”

Trump laid out for the first time in detail the elements of what will be the second chapter of his 2016 bid, signaling an evolution toward a somewhat more traditional campaign. Trump is preparing his first television ads with a media firm that is new to politics. Melania, his wife, and Ivanka, his daughter, are planning public appearances highlighting women’s health issues to help close Trump’s empathy gap with female voters.

Trump is also publishing a book and planning to roll out policies on reforming the Department of Veterans Affairs and on trade and China’s currency manipulations. And he is deepening his political organization far beyond the early states, with top advisers vowing that his fight for the nomination will go all the way to the floor of the Republican National Convention.

Trump, who is mostly self-funding his campaign, said he had originally budgeted up to $20 million through mid-September for television advertising. But so far he has not spent anything to go on the airwaves, since he is so often on them: “It’s been all Trump, all the time. . . . If you had an ad, people would OD.”

But he and his aides said that would soon change. His campaign says it has hired a Florida-based advertising firm, and Trump said he has proposed several concepts for ads in the works.

“I have such a great concept — in fact, so good,” Trump said, declining to specify.

Campaign manager Corey Lewandowski said Trump’s team would probably spend considerably more than $20 million on paid media later this year — “whatever it takes.” He said the spots would be “nontraditional,” saying the firm, which he and Trump declined to name, has never created political ads.

Central to the fall strategy is the release later this month of a book that will serve as a campaign manifesto. During the interview, Trump showed off the cover and title, “Crippled America,” and held up pages of the galleys, which he was editing by hand. “It’s actually the hardest I’ve worked on a book since ‘The Art of the Deal,’” he said, referring to his 1987 bestseller. “I don’t want to have a stupid statement in the book that people are going to say, ‘Hey, why did he say that?’ ”

Trump said he does not believe the next stage of the campaign will require him to change his flamboyant, confrontational style, which has captivated the attention of voters whether they support him or not. But he noted that running for president has brought pressures and demands that he did not experience in the business world and had not anticipated in the political arena.

During a campaign rally in Waterloo Iowa, Donald Trump vowed to win the presidency saying, "I'm not going anywhere." (Reuters)

“It’s very unforgiving,” he said. “If you make a mistake that can be very easily explained, it can still be turned around and then you have three bad days of press over something that actually wasn’t even a big deal.”

Trump said he doesn’t want to significantly tinker with how he presents himself to the public. As Lewandowski put it, Trump “remains Trump.”

“It’s going to be the same thing,” Trump said. “You’ve got to have a personality. You’ve got to be able to speak your mind. You’ve got to have some thoughts that are correct.”

Trump said he is readying for an eventual winnowing of the Republican field, but he disagreed with some predictions that the contest will narrow to just two or three finalists for the nomination. “I think you’ll go past New Hampshire and you’ll have four or five people left,” he said.

His advisers are working to assure that Trump will qualify for the ballot in all 50 states and the U.S. territories — an arduous and time-consuming task that has caused some first-time candidates to stumble. Lewandowski said the campaign has hired a company that will work only for Trump to meet the state-by-state requirements. Virginia is among the most difficult states, but Lewandowski said Trump will be qualified there by the end of this month.

“I’ll be happy to be the under­estimated campaign,” Lewandow­ski said. “If I don’t get Mr. Trump on the ballot, which is the nuts-and-bolts part of my job, I should be fired immediately.”

Trump’s campaign headquarters is on the fifth floor of Trump Tower here, in an industrial space that previously had been a construction area and hangout for the crew of NBC’s “The Apprentice.”

The main room is a showcase for Trump’s penchant for boastful teasing: A “wall of shame” features downcast photos of the two candidates who have dropped out, Wisconsin Gov. Scott Walker and former Texas governor Rick Perry. It also highlights his proclaimed frugality, as aides work at plastic picnic tables and sit on folding chairs.

Compared with the bustling Brooklyn headquarters of Democrat Hillary Rodham Clinton, with hundreds of staffers on the payroll, Trump’s Manhattan command center is barren. Lewandowski said about a dozen aides are at the location, including political director Michael Glassner and spokeswoman Hope Hicks.

Trump has between seven and 12 paid staffers in each of the first three voting states — Iowa, New Hampshire and South Carolina — and is hiring in Florida, Georgia, Tennessee, Texas and other states. Lewandowski said Trump enjoys a “massive grass-roots network,” allowing volunteers to feed local intelligence on rival campaigns to New York.

Asked if he had discussed an exit plan with Trump should the candidate slip in the polls, Lewandowski said he had not: “We’re going to the convention — that’s it. One delegate or 2,000 and change, we’re going to the convention, and there’s nobody who can get him out of the race.”

From behind his desk, with Central Park over his shoulder, and with no television cameras rolling, Trump presented a less strident and combative persona than the one that has become a familiar presence on television. He was conversational and at ease, even introspective at times, while still displaying high sensitivity to perceived slights and unfair media coverage.

Trump held up last weekend’s New York Times Magazine, which included a cover he did not like of a cartoonish Trump as a rising balloon. Then he flipped to an inside page with a black-and-white portrait of him intensely pointing his finger at the camera. “Look at this,” he said, arguing that the photo should have been on the cover. “It’s the greatest picture I’ve ever had.”

During a tour of his office suite, Trump — ever aware of his image — laughingly declined a reporter’s request to pose for a photograph holding up an oil painting of himself that he said had been sent by a supporter. “You’d make me look so bad!”

The interview did not focus on his opponents, and Trump spent almost no time talking about them. He has often said he is a counterpuncher who attacks primarily when provoked. But he appears to have at least one exception: Mitt Romney. Asked about recent criticism from the 2012 GOP nominee, Trump made clear he fired the first shot. “I don’t blame him because I’ve been very tough on Romney,” he said. “He’s a choke artist.”

Trump claimed credit for keeping Romney out of the 2016 race, though he bowed out long before Trump ever became a candidate. Dismissing the suggestion that it was former Florida governor Jeb Bush’s fundraising prowess that kept Romney from the race, Trump insisted: “He got scared away by me! By my mouth.”

Throughout the interview, Trump exuded customary aplomb but nonetheless indicated there are aspects of his performance that he can improve. He said he sensed he had won the first debate outright but suggested the second debate had been less satisfying.

“I was angry about the second debate,” he said, complaining about the overheated room and that three hours was one hour too many. “You can’t hold people’s attention,” he said. “ ‘Gone With the Wind’ was three hours, okay?”

He countered criticism that he had almost disappeared during much of the final hour. “People said, ‘Oh, he faded at the end,’ ” Trump said. “I didn’t fade. They didn’t ask me any questions. Now, I could have butted in like some people were doing, but I didn’t think it was appropriate.”

Trump said that in the next debate, which will be held Oct. 28 in Boulder, Colo., he will change tactics and insert himself more energetically in an effort to put questions about his previous performance to rest.

Trump’s candidacy has been fueled by his loud swagger and his hard-line views on immigration. But in the coming weeks, he hopes to bolster and reorient his message with an eye toward blue-collar voters.

“I’m a person who is capable of going into far greater detail than any of my opponents,” he said, an assertion likely to be tested by rivals. But he said the calls for him to do so come mainly from reporters and pundits: “I’ve never had a voter stand up and say, ‘Could you release policy papers?’ ”

A major component will be a tough new approach to China, which he said has “emasculated” the United States through trade and currency manipulation.

“I’ve been working hard on the China thing,” Trump said. “It’s astronomical what they have done to our country, to destroy the economics of our country. Astronomical. It’s the greatest theft in world history.”

Trump’s competitors have suggested that he has little depth on international affairs. After being ridiculed for saying this summer that he gets much of his foreign policy advice by watching military experts on television talk shows, Trump has begun to seek counsel from some generals directly, Lewandowski said.

The strife in Syria has become a staple of Trump’s stump speech, and it is an area where he has begun to differentiate himself from others in his party with a stance that sounds decidedly more cautious. In the interview, he questioned those who are advocating more direct military intervention by the United States.

“They basically want to start World War III over Syria,” he said. “If we’re going to have World War III, it’s not going to be over Syria. . . . I won’t even call them hawks. I call them the fools.”

Immigration continues to be the issue that has largely defined his candidacy, though he said in the interview he was surprised at the strength of the response he has gotten with his inflammatory language about Mexican “rapists” and criminals. “I had no idea it was going to resonate in the way it has,” he said.

Trump also said he plans to talk even more about the role of money in politics and what he described as an incestuous relationship between candidates, the donor class and their allied super PACs.

Looking to boost his favorability with women, Trump plans to spotlight his wife and daughter, whose passion for women’s health issues could help soften the candidate’s edges. Asked if they shared his opposition to abortion, Trump demurred. “I’m going to let them reveal themselves if people are going to ask that question, which they might not,” he said.

Glancing at an office wall covered in mementos and awards, Trump picked up a campaign bumper sticker featuring his name in thick red letters. “A hot ticket,” Trump declared, smiling proudly.

“I believe in the power of positive thinking,” he said, “but I never like to talk it. It’s never in sight until you win it. You know, there are a lot of minefields out there.”