As wealthy donors supporting Hillary Clinton pummel Donald Trump with negative ads, the Republican presidential candidate's own backers are struggling to return fire, hurt in part by a late start and conflicting signals from the campaign. In the latest setback, Thomas Barrack, a billionaire Los Angeles investor who said last month he'd gathered $32 million in commitments for a new super-political action committee supporting Trump, has decided not to donate to it or any other super-PAC, according to "Papa" Doug Manchester, a leading Trump fundraiser in California who has discussed the project with Barrack. The group raised only about $2 million through the end of June, according to Yahoo News.

"Tom Barrack and I just decided we would support the campaign to the maximum we can," Manchester said in an interview this week, referring to the roughly $450,000 maximum that an individual can donate to Trump and his party through a joint-fundraising committee. (A married couple can contribute $900,000.) That's a far cry from the multi-million-dollar checks that Barrack suggested last month were flowing to the super-PAC he was promoting, known as Rebuild America Now. Through a spokeswoman, Barrack declined to comment. 

Rebuild America Now is one of more than a half-dozen super-PACs jockeying for donors, so far without any emerging as the undisputed leader. As of the most recent reports filed with the Federal Election Commission, none had raised more than $3 million, while the main PAC supporting Clinton had amassed more than $88 million and is now spending around $4 million a week on anti-Trump messages. The groups are due to disclose updated figures over the next week.

Trump didn't begin actively soliciting funds for his campaign until May. And after winning the Republican primaries without major advertising campaigns, he has repeatedly expressed ambivalence about whether large-scale spending is even necessary. In private conversations with donors, top campaign officials have sometimes given conflicting signals about which super-PAC they prefer, according to people familiar with the matter who spoke on condition of anonymity. And Trump has sent mixed messages about whether he wants the support of super-PACs at all.

Earlier this year, the Las Vegas casino mogul Sheldon Adelson told Trump he'd give $100 million to support the presidential bid and explored forming his own super-PAC to direct the spending. But Adelson isn't currently pursuing his own super-PAC, according to Andrew Abboud, a top Adelson aide, confirming an earlier report in the Los Angeles Times. A spokesman for Adelson declined to comment on whether Adelson is sticking with the $100 million pledge.

The most recent super-PAC to enter the scene is Defeat Crooked Hillary, run by David Bossie, a longtime critic of the former secretary of state. The group is actually a repurposed PAC, originally formed by the New York hedge-fund manager Robert Mercer to support Senator Ted Cruz's presidential bid. The group had about $1.3 million left over at the end of May, and Bossie said that since then, Mercer made a "substantial" additional seven-figure contribution.

"You've seen what he's done in the past. He just doesn’t do things small," said Bossie. Mercer spent $13.5 million supporting Cruz and is already the second-biggest political donor of the 2016 election cycle, according to the Center for Responsive Politics.

Defeat Crooked Hillary started operations only last month and has disclosed just $20,000 in media spending since then. Bossie said he's still getting organized and will be meeting with donors and developing plans in the coming weeks. He said donors are interested in contributing, in part because the Trump campaign supports the effort. Mercer's seed money will cover all the overhead costs of running the group, so that "100 cents on the dollar" of outside contributions will go directly to anti-Clinton messages, Bossie said.

One of the oldest groups supporting Trump, formed in January and known as Great America PAC, probably won't meet a goal announced in May of raising $15 to 20 million by the Republican National Convention next week in Cleveland, said Eric Beach, a PAC official. He said it might be able to get close by the end of the month. It had gathered only $2.5 million as of May 31.

Beach said the group raised $2.5 million in June and another $1.6 million in the first 10 days of July, including donations of $250,000 from the family of Hank Seale, an Austin entrepreneur, and $150,000 from Doug Lebda, the founder of LendingTree in Charlotte, North Carolina. The group is investing in voter-turnout efforts in addition to pro-Trump TV ads.

"We've identified millions of people who support Trump. Now we're raising the appropriate funds to make sure these people vote in November," he said.

As for Barrack, he remains a key supporter of Trump and is scheduled to speak at the convention next week. "He loves Donald Trump just like I do. He wants to do everything he can to help him get elected," said Manchester, adding that he planned to co-host a fundraising event in San Diego for Trump's joint-fundraising committee that was expected to raise $4 million.

But Manchester said that he and Barrack  had been turned off by the idea that super-PACs spend much of their money on negative TV ads. "Tom Barrack is not a negative person and neither am I. We want to speak on the merits."

Last month, Yahoo News reported that Barrack was backing off from raising money for the super-PAC because of pressure from business partners in China. The Barrack spokeswoman declined to comment on that report. Officials at Rebuild America Now didn't respond to inquiries.

Some donors have been confused by Trump's posture toward super-PACs. He often ridicules his opponents for depending on their support, and boasts that his wealth makes them unnecessary. During the Republican primary, he mostly depended on free TV news coverage and his own money to get his message out. But last year, he also appeared at an event set up by a super-PAC working on his behalf. Later, he disavowed the group and it disbanded. In March, his campaign sent a strongly-worded letter to Great America PAC, asking it to stop using his name in fundraising activities.

After he vanquished his Republican primary opponents in May, Trump softened his stance on fundraising and took steps to raise money from wealthy donors through a joint-fundraising agreement with the Republican party. He announced last week that those efforts had reaped $51 million for his campaign and the party since late May. Those groups, however, cannot accept contributions of unlimited size from individuals and corporations the way super-PACs can.

In private conversations with Trump campaign officials, some donors have gotten the impression that Defeat Crooked Hillary is a preferred destination for donations, while others have been directed to Rebuild America Now, the people familiar the conversations said. Still others have been waiting to see where big-spending donors like Adelson put their money.

Nevertheless, last month, one of Trump's top aides said the candidate remains steadfastly opposed to support from these groups. 

"He doesn’t want it. He's actually gone out of his way to shut down super-PACs that have started to use his name," said Michael Cohen, a top Trump lawyer, during a forum organized by Bloomberg Politics in New York. "I can call Sheldon Adelson tomorrow and he'll give me $100 million. He's offered. I have a half a dozen people exactly the same. Doesn’t want to do it. He does not want a super-PAC."