Donald Trump speaks at a campaign event at Trump Doral golf course in Miami.

Donald Trump speaks at a campaign event at Trump Doral golf course in Miami. Carlo Allegri/Reuters

Businessman Donald Trump officially became the Republican nominee at the party’s convention in Cleveland.

Just days into his new role as the presumptive Republican presidential nominee, Donald Trump is walking away from key positions that have defined his anti-establishment bid — including his pledge to keep wealthy donors at bay.

The New York real estate tycoon, who frequently boasted throughout the primary race that he was financing his campaign, is setting up a national fundraising operation and taking a hands-off posture toward super PACs.

He is expressing openness to raising the minimum wage, a move he previously opposed, saying on CNN this week, “I mean, you have to have something that you can live on.”

And Trump is backing away from a tax plan he rolled out last fall that would have given major cuts to the rich. “I am not necessarily a huge fan of that,” he told CNBC. “I am so much more into the middle class, who have just been absolutely forgotten in our country.”

The billionaire’s tendency to change his mind on policy matters is a hallmark of his unconventional campaign — a quality he casts as an asset, saying it shows he is open to new ideas. Even so, his latest reversals are striking, particularly when it comes to the financing of his presidential bid, a central part of his pitch to voters.

The presumptive Republican presidential nominee reversed course on a whole load of issues — all on May 4. (Peter Stevenson/The Washington Post)

They also come amid an escalating battle between Trump and many Republican establishment figures, who blanch at his combative tone and controversial policy positions. House Speaker Paul D. Ryan (Wis.), the country’s highest-ranking elected Republican, said Thursday that he was not ready to endorse Trump as the nominee; Trump responded that he would not endorse Ryan’s proposed policies.

[Paul Ryan declines to support Donald Trump: ‘I’m not there right now’]

Throughout the primary contest, the Manhattan mogul bragged that he was the only contender unencumbered by alliances to rich backers. Even though he has been accepting donations ($12 million worth through the end of March), Trump’s proclamation of financial independence fed a sense among his supporters that he alone was standing outside a corrupt process.

The candidate furthered that impression by regularly denouncing his opponents for leaning on super PACs, which can take unlimited contributions, and by disavowing groups that cropped up to support him.

But Trump expressed little concern this week that a super PAC called Great America PAC was emerging as the vehicle of choice for wealthy Trump supporters, and he praised one of the group’s advisers, longtime Republican consultant Ed Rollins.

“I know that people maybe like me and they form a super PAC, but I have nothing to do with it,” the candidate said Wednesday on “NBC Nightly News,” adding, “So we’ll see what happens.”

He also acknowledged that he cannot personally cover the cost of a general-election campaign for the next six months, unless he is willing to “sell a couple of buildings,” as he said on MSNBC’s “Morning Joe.”

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On Thursday, Trump tapped hedge-fund manager and film investor Steven Mnuchin to assemble a national fundraising operation, tasked with raising at least $1 billion for the general election. That will probably require the creation of a traditional bundling effort, in which rich supporters are offered perks for collecting checks from their friends and family members.

Although the campaign said that Trump still plans to put “substantial money” into his bid, the first-time candidate will be seeking support from the very donor class he has vilified.

If Trump “makes it clear he wants to change the rules but he’s stuck playing under them, I don’t think there will be a big turn-off,” said conservative political consultant John Pudner, whose group Take Back Our Republic seeks to reduce the influence of the wealthy in politics. “But if it looks like he’s just abandoning the one thing that got him here, I think there’ll be trouble.”

Selecting Mnuchin to lead the effort is a particularly jarring choice for a candidate who has lambasted hedge-fund managers on the trail. The chief executive of Dune Capital spent 17 years at Goldman Sachs, including a stint as head of the bank’s mortgage department, according to Bloomberg News.

[Trump campaign announces national finance chairman with ties to Wall Street and Democrats]

When asked if Trump was undercutting his pledge to be independent of big donors, spokeswoman Hope Hicks responded in an email: “Mr. Trump is not raising money for his own campaign. He is raising money for the party.”

She did not respond to an inquiry about whether any of the money Mnuchin will help raise will go into Trump’s campaign coffers.

The Republican National Committee has been counting on getting robust fundraising assistance from its nominee to finance its quadrennial get-out-the-vote efforts — massive operations that lift not only the White House nominee but down-ballot candidates across the country.

In 2012, Republican nominee Mitt Romney and the RNC together raised $493 million through a joint committee. The effort was primarily driven by the expansive donor network that the former Massachusetts governor had cultivated over the years — so much so that RNC finance staffers relocated to Romney’s Boston headquarters to work with his fundraising team.

It remains to be seen whether the Trump campaign’s prospective donor list will prove valuable.

“The Trump campaign has made it very clear they intend to do everything they can to help the team,” said RNC communications director Sean Spicer, who added that the campaign plans to provide a list of supporters “who have been very active in their campaign, and a vast network of business people and others who could be very helpful to us.”

Already, some fundraisers who had backed other candidates have signed on. Mica Mosbacher, a former RNC finance co-chairman who helped Sen. Ted Cruz (Tex.) tap donors across the country, said she plans to assist the party effort.

“I plan to support Donald Trump as our nominee and help the RNC fundraise and am calling on conservatives to unite,” she wrote in an email.

[Bushes’ snub of Trump has roots in Republican base anger]

But even wealthy contributors who said they were supportive of Trump expressed surprise that he was going to begin soliciting donations.

“I thought he was self-funding,” said Dallas investor Doug Deason, whose father, billionaire technology entrepreneur Darwin Deason, financed super PACs supporting Cruz and former Texas governor Rick Perry.

And there is still substantial resistance to Trump among key segments of the party’s major donor base.

“It’s going to be hard to ask people for money for someone who says he’s so rich he doesn’t need people’s money,” said Republican fundraiser Lisa Spies, who led Romney’s finance outreach to women and the Jewish community and helped raise money this cycle for former Florida governor Jeb Bush.

Trump’s hiring of a finance chairman was a good first step, she said, but she added that “he’s going to spend his time mending fences with donors. I think he’s got a very tough job in front of him.”

The key for many bundlers, said Fred Malek, who served as Sen. John McCain’s national finance chairman in 2008 and was a major fundraiser for Romney in 2012, will be whether Trump alters his provocative approach.

“It really is going to depend on the tone he and his campaign takes,” Malek said. “If he is able to be more welcoming and inclusive and bring more people in his orbit, that will go a long way.”

Jose A. DelReal contributed to this report.