NEW YORK (AP) — Donald Trump is taking his first steps toward raising the massive amounts of money needed for a national presidential race, aiming to broaden his primary insurgency into a full-fledged general election campaign and unite the fractured Republican Party behind him.

Trump is reaching out to party heavyweights, hoping to repair his at-times strained relationships with the Republican National Committee and big GOP donors whom he bashed repeatedly during the primaries.

On Thursday, his campaign named a finance chairman, Steven Mnuchin, who is chairman and chief executive officer of Dune Capital management LLC, a private investment firm, and previously worked at the New York bank Goldman Sachs. Mnuchin "brings unprecedented experience and expertise" to the fundraising operation, the campaign said.

Trump's new efforts include taking pains to reassure party leaders that he wants to help Republican Senate and House candidates, some of whom have expressed major concerns that Trump at the top of the GOP ticket will be a drag on their own campaigns.

Earlier this week, Trump's final GOP foes, Ted Cruz and John Kasich, suddenly dropped out, clearing his path to the nomination. But some of the party's big names are still keeping Trump at arm's length. Neither former President George W. Bush nor Mitt Romney, the 2012 GOP nominee, plans to attend the party's national convention in July.

Members of the celebrity businessman's campaign were to meet with the party's national committee and enter a joint fundraising agreement needed for both his bid and for Republicans to maintain control of Capitol Hill, aides said.

"In order to really govern, we need majorities in the House and Senate. We're going to work with the party to raise money for down-ballot races to be successful," said Corey Lewandowski, Trump's campaign manager, in an interview Thursday.

Trump, a billionaire who paid for most of his primary campaign by himself, acknowledges he would have to sell some of his holdings to muster the hundreds of millions of dollars for a general election bid, something he said he doesn't necessarily want to do.

He said Thursday in a statement that he would be "putting up substantial money toward the general election," following the $36 million in loans he previously made.

Yet he's also beginning to take a more traditional route for his likely battle with Hillary Clinton, a Democratic fundraising powerhouse.

Mnuchin, who has never led a major political fundraising team, faces a gargantuan task.

Many major GOP donors have never heard of him. Like his new boss Trump, Mnuchin has a record of giving both to top Republicans and Democrats — including Clinton during her 2008 presidential run.

Trump hopes to tap into the RNC's existing fundraising network, but some of the party's big donors are reluctant to embrace him.

"High-dollar donors need to be convinced that Trump is going to be a serious candidate and won't embarrass them," said Charlie Spies, a veteran Republican operative with deep ties to party fundraisers.

This is all new to Trump. Through the end of March, he had raised $12 million, mostly from fans who clicked the "donate" button on his website or bought wares such as the ubiquitous red ballcap emblazoned with his slogan, "Make America Great Again," campaign finance documents show.

That contrasts with Clinton, who has raised some $187 million so far and began her general election fundraising effort back in November by setting up a "victory fund" that can solicit huge checks for her campaign, the Democratic National Committee and state parties.

Clinton is spending the better part of this month on a fundraising, including stops in New York, Michigan, California and Texas. Trump, as of Wednesday night, had not a single fundraising event on the books.

The differences don't end there. A pro-Clinton super political action committee that can take unlimited donations from wealthy individuals, companies and unions has already reserved some $90 million worth of advertising for the general election. Great America, which is shaping up to be the main pro-Trump super PAC, was almost $1 million in debt at end of March.

Ed Rollins, who ran Ronald Reagan's 1984 campaign, hopes to change that. He joined Great America as a senior strategist and said on a super PAC conference call Wednesday. "We're going to figure out what the Trump campaign needs and can't do by itself," Rollins told callers.

Trump's lean campaign team will likely depend heavily on the RNC as he shifts to the 50-state task ahead. Yet the national committee is also counting on Trump to reciprocate by helping to fund its nationwide data operation and staffing expansion.

RNC members note that Trump has attracted many new voters to the party, who would likely be willing to give money. It's unclear, however, whether he can attract enough elite donors capable of writing checks upward of $350,000, Spies said.

Trump will also name a transition team and a vice-presidential search committee. He says he has not truly begun the VP vetting process but will favor a Washington veteran.

Said Lewandowski: "When a complete outsider is picked to lead the ticket, it makes sense to have someone with government experience on it. He wants a strong executive who has a leadership role in D.C."

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Bykowicz reported from Washington. Steve Peoples contributed reporting from Washington.

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Contact Jonathan Lemire on Twitter at http://twitter.com/JonLemire