Republican presidential candidate Donald Trump's campaign raised just $3.1 million in May, while Democratic rival Hillary Clinton brought in $27 million. Here's a breakdown of the two campaigns' finances. (Jenny Starrs/The Washington Post)

As top Republicans expressed astonishment and alarm over Donald Trump’s paltry campaign fundraising totals, the presumptive nominee blamed party leaders Tuesday and threatened to rely on his personal fortune instead of helping the GOP seek the cash it needs.

New campaign finance reports showing that Trump had less than $1.3 million in the bank heading into June ignited fears that the party will not be able to afford the kind of national field effort that the entire Republican ticket depends on.

The real estate mogul responded by going on the offensive, saying GOP fundraisers have failed to rally around his campaign.

“I’m having more difficulty, frankly, with some of the people in the party,” Trump said on NBC’s “Today,” adding, “They don’t want to come on.”

“If it gets to a point,” he said, “what I’ll do is just do what I did in the primaries,” when he lent his presidential campaign more than $43 million.

The billionaire developer increased his line of credit to the campaign by an additional $2.2 million last month — the smallest amount he has shelled out this year — but Trump said in a statement Tuesday that “if need be, there could be unlimited cash on hand as I would put up my own money.”

It’s unclear how quickly he could access the hundreds of millions needed to finance a national campaign. In May, Trump suggested that to do so, he would have to “sell a couple of buildings.”

If he did tap his wealth to finance his bid, it would effectively amount to abandonment of the Republican National Committee and the rest of the GOP ticket, which relies on the presidential nominee to help fund a national field organization for the fall elections.

GOP strategist and fundraiser Austin Barbour said if Trump fundraising does not pick up, it “could have a devastating impact” on the Republican Party.

“If they don’t fix this in a massive way, it’s going to have widespread implications down the ballot. It just is,” Barbour said. “If he’s not raising hundreds of millions of dollars, there are gubernatorial races, Senate races, congressional races, attorney general races, you name it, that will be impacted. Those races are dependent upon get-out-the-vote efforts from the RNC and the presidential campaign.”

The Trump campaign released a statement touting its fundraising as “incredible,” saying there has been “a tremendous outpouring of support” since the candidate held his first finance event May 25. Its joint fundraising committee with the RNC is expected to bring in at least $20 million in June, with $6 million coming from a high-dollar dinner in New York on Tuesday night, according to a person familiar with the figures.

The vast share of the money will go to the national party committee. GOP officials said the party already has nearly 500 field staffers deployed around the country and noted that the RNC has outraised its Democratic counterpart by $46 million during this cycle.

But top Republicans said Trump squandered the month of May by neglecting to capitalize on clinching the nomination to build and activate a grass-roots fundraising base.

There is also growing scrutiny of his heavy use of Trump-owned companies as vendors. Of the $63 million his campaign spent through May, more than $6 million — close to 10 percent — went to pay Trump properties or reimburse Trump and his family for expenses, according to an analysis by The Washington Post. That includes $4.6 million paid to his private jet company, TAG Air, and $423,000 that went just last month to his Mar-a-Lago Club in Palm Beach, Fla.

The Trump campaign did not respond to questions about the payments.

Meanwhile, expected Democratic nominee Hillary Clinton has been stockpiling cash. She raised more than $28 million in May and started June with $42 million in the bank. The former secretary of state has held a string of high-dollar fundraisers in the past several weeks, including three hosted by wealthy donors in New York on Monday night.

Trump is “now looking into the abyss,”said Ed Rollins, the top strategist for Great America PAC, a pro-Trump super PAC. “He can either start writing checks and selling some buildings and golf courses or get on the phones and talk to donors. Big donors just don’t want to give money unless they have the opportunity to talk to the candidate, hear what your positions are. There’s just been a failure from start to finish on the fundraising side.”

Lisa Spies, a veteran GOP fundraising consultant, said she has been amazed at the lack of outreach from Trump.

“No donors that I deal with — and I deal with national Jewish and women donors — none of them has gotten a phone call. None. Not one,” Spies said. “To raise money, you have to ask for money. It’s that simple. Whether you ask for it by mail, whether you do phone calls, whether you do events, whether you have one-on-one meetings, you have to ask.”

Among those who had yet to receive a call was Fred Malek, the well-connected finance chairman of the Republican Governors Association.

“Many leading donors are waiting to see him take a more inclusive, tolerant and substantive approach to campaigning,” Malek said. “Even if they all came around with great enthusiasm, there’s no way in this short time frame that’s available he can build the kind of organization that will be competitive financially. There’s no way he can do it. Hillary Clinton’s been at this for several decades.”

One prominent Washington fundraiser who has played major roles on past Republican presidential campaigns said he has not heard of Trump reaching out to any of his peers.

“I have not been asked, and I don’t know anybody in town who has been asked,” said this person, who spoke on the condition of anonymity in order to talk candidly. “There is absolutely no discernible presence in D.C. raising on his behalf. And I’m guessing this is not unique to D.C. They are so [expletive] far behind the curve on so many things that are Campaign Organization 101, I find it inexplicable.”

The problems have spilled over to the RNC, which took on $2 million in additional debt in May, underscoring how Trump’s failure to build a fundraising structure has put financial pressure on the national party committee.

“Trump’s fundraising is shockingly thin and has created a dark cloud over his ability to be financially competitive with the Clinton machine,” said Scott Reed, a veteran GOP operative and top strategist for the U.S. Chamber of Commerce. “While the finance numbers are weak, this is nothing a smart VP choice, an exciting, substantive convention and a strong first debate performance cannot overcome.”

Mica Mosbacher, a longtime party fundraiser who helped arrange finance events in Texas last week, including one in Houston that brought in $2 million, said that some donors loyal to Trump’s vanquished primary opponents have been slow to embrace the mogul.

“I think we’ve got a few holdouts and possibly supporters of other candidates still licking their wounds,” she said. “But I see people coming on board.”

Other Republican financiers were more pessimistic. Trump has resisted making fundraising calls to major donors and is uncomfortable soliciting support because he is so accustomed to being wooed himself, according to people familiar with the situation. Some of the party’s most reliable bundlers have declined to sign on to the fundraising operation. And the campaign’s bare-bones staff has also been slow to schedule dates for finance events around the country.

Many downballot Republican strategists and donors were in a state of shock Tuesday, saying privately that while they expected Trump’s war chest to be small — perhaps in the range of $10 million — they never thought he would enter June with just $1.3 million in the bank.

GOP strategists were particularly exasperated that Trump has been slow to tap into his fervent base of supporters for small donations online, potentially leaving tens of millions of dollars on the table over the last month.

“There’s no question that if Ben Carson could raise an enormous amount of money from the conservative base, that he could have,” Rollins said, referring to the retired neurosurgeon who ran a strong grass-roots fundraising operation as a GOP presidential candidate. “He has millions and millions of supporters, but early on, he pooh-poohed all of that.”

Trump on Tuesday sent what he touted as his first fundraising email. (It wasn’t: A joint fundraising committee he has with the RNC sent an email solicitation in his name on June 8.)

“I’m going to help make it the most successful introductory fundraising email in modern political history by personally matching every dollar that comes in WITHIN THE NEXT 48 HOURS, up to $2 million!” Trump wrote in Tuesday’s missive.

It was unclear whether he means to actually donate additional funds or continue to loan cash to his campaign. The billionaire has now lent his campaign $45.7 million and given it $400,000 more, while collecting $17 million in contributions.

Trump also helped bring in $3 million for the RNC through Trump Victory, a joint fundraising committee set up at the end of May.

However, a large share of that money — $1.8 million — is earmarked for new party accounts to pay for convention, legal and headquarters expenses.

The party raised $11 million in May and ended the month with $20 million in the bank — but also nearly $7 million in debt, up from almost $5 million at the end of April.

Sean Spicer, the RNC’s communications director, said the party’s increased line of credit was typical for this point in an election year, adding that party officials were optimistic about fundraising.

“This report only reflects one week of the joint fundraising agreement, and I think as we continue to ramp up, you’re going to see continued enthusiasm from donors around the country,” he said.

Still, the RNC is in a starkly different place compared to four years ago. In May 2012, the national party scooped up more than $34 million, ending the month with more than $60 million in the bank and $9.9 million of debt. Nearly $26 million that month came through Romney Victory, a joint fundraising effort between the party and the 2012 nominee, Mitt Romney.

Anu Narayanswamy and Sean Sullivan contributed to this report.