Republican donors, still dubious of Donald Trump’s prospects in the general election and annoyed by his taunts during the primary, are keeping their wallets closed en masse even as the celebrity businessman has begun to court them.

The collective skepticism of the party’s most active donors was reflected starkly in Trump’s campaign finance report released Monday, which showed just $1.3 million on hand as of the end of May — nearly one month after he locked up the Republican nomination. Hillary Clinton, for her part, has amassed a $42 million war chest for the general election, in spite of a primary contest that dragged on until this month.

Republican consultant Ed Rollins, who co-founded the pro-Trump Great America super PAC, said the anemic fundraising suggests Trump’s candidacy is in “big trouble.”

“Being perfectly honest, I used to be chairman of a congressional committee, and if I had a House race today that basically came in with that kind of figure in June, I’d take them off the target list,” Rollins told Fox Business on Tuesday.

“Fundraising is a problem,” another Trump ally acknowledged to RealClearPolitics. “Who gives money to a billionaire?”

Trump’s fundraising woes stem from a few factors, according to several Republicans in the fundraising sphere who spoke with RCP. Like many GOP elected officials, party donors have balked at Trump’s polarizing remarks in the past few weeks, when they hoped he would reorient his message for the general election. They remain put off by Trump’s invective targeting donors and their favored candidates during the primary. And they await any signal from Trump that he will invest substantially in growing his campaign.

Trump “spent the past year attacking donors and saying he didn’t need them and he would self-fund,” said Charlie Spies, former treasurer and counsel to the pro-Jeb Bush super PAC, Right to Rise. “Now to do a 180 and say he does want their money is a hard transition.”

“He should put $100 million to $200 million of his own money into his campaign now,” Spies added. “That would send a message to donors that he is serious about this race and is invested in winning.”

Trump’s wealth has indeed appeared to complicate and even hamper his fundraising efforts. As he asks for financial support from wealthy donors, Trump has continued to suggest he could independently bankroll his general election operations — leaving many donors to wonder why they need to invest in his campaign.

“If need be, there could be unlimited ‘cash on hand,’ as I would put up my own money, as I have already done through the primaries, spending over $50 million,” Trump said in a statement Tuesday.

Trump did not spend nearly $50 million during the primary, but lent his campaign that money — just as Mitt Romney did in 2008, when he lent $44 million to his primary campaign. Trump, however, has insisted he will not seek to reimburse himself.

"I have absolutely no intention of paying myself back for the nearly $50 million I have loaned to the campaign,” Trump said in a statement last month to ABC News. “This money is a contribution made in order to Make America Great Again.”

But donors remain wary of the loans, which Trump has not officially forgiven, and of Trump’s spending practices on the campaign, including paying for travel for his children and hosting events at Trump properties, an arrangement that results in the campaign paying Trump and his companies.

Meanwhile, as some of Trump’s foremost former rivals have withheld their support for Trump, many of their donors have followed their lead and remained on the sidelines.

“The two largest fund raisers in the primary were Jeb Bush and Ted Cruz, and Donald Trump attacked both of them and their families personally, and neither of them are actively supporting Trump,” said Hal Lambert, a former national finance co-chair for Cruz. “And many of their donors are not going to actively support Trump.”

Nor has Trump wooed these donors in the manner or with the intensity that a presumptive nominee for president normally would. His campaign so far has not tempted donors with choice seats or party invites at the convention, as Romney did during this time in 2012, Spies said. And Trump, someone who documented his affinity for non-stop phone calls in “The Art of the Deal,” has not been burning up the phone lines for money, either.

“He’s not your typical politician who dials for dollars every day,” Ray Washburne, a vice-chairman for Trump’s joint fundraising committee with the Republican National Committee, told Politico earlier this month. “He’s not hitting the phones every day.”

Since agreeing last month to establish the joint fundraising committee with the RNC, Trump has headlined roughly a dozen fundraisers, most of which were not reflected in his May report. On Tuesday he hosted a dinner at Le Cirque restaurant in New York City, attended by the Wall Street set.

But it’s unclear how deep the commitment of these donors runs, even among Trump’s own fundraising team. Of the original 19 chairs, vice-chairs and trustees of Trump’s joint fundraising committee, none are listed as donors in his most recent campaign finance report.

As an alternative to soliciting large donations, some Republicans are suggesting that Trump consider a fundraising system that worked for another Clinton rival. Bernie Sanders raised tens of millions of dollars from small donations during the Democratic primary, enabling him to keep pace with Clinton without linking him to the “millionaires and billionaires” he publicly denounced.

“There is no reason why Trump cannot replicate the Sanders model,” said Eric Fehrnstrom, a former senior adviser to Mitt Romney. “That needs to be Trump's focus — not the skeptical donors on Wall Street, but the millions of ordinary folks who want to see him win.”

As Trump has fumbled with the keys to start his fundraising engine, however, Clinton has sped ahead. So far in June, pro-Clinton groups have spent nearly $24 million to advertise in battleground states, while Trump’s campaign and his allies have spent nothing in defense.

“Every week that goes by when you’ve got unanswered attacks in target states makes it harder to win,” Spies said.