Much of Donald Trump's fundraising haul in June appears to have come in the last 10 days of the month, after he began fundraising online in earnest. (David Zalubowski/AP)

This post has been updated.

Donald Trump raised more than $26 million through online and mail solicitations in June and another $25 million at events with the Republican National Committee, his campaign announced Wednesday, a hefty haul that his allies hope will put to rest anxieties in the party about his fundraising prowess.

The combined $51 million falls short of the $68.5 million that Democratic contender Hillary Clinton and the Democratic Party collected in June, which included $40.5 million she raised directly for her campaign. But it was the biggest monthly take by far for the presumptive GOP presidential nominee, who did not begin to hold fundraising events until late May. And it suggests Trump has the ability to quickly inject large sums of money into his campaign coffers by tapping into the fervor of his supporters.

Much of the campaign's money appears to have come in during the final 10 days of the month, when Trump’s operation began aggressively soliciting money online for the first time. The Trump campaign announced Wednesday that more than 400,000 supporters made donations in June, with more than $3 million coming in just one day. That indicates that the billionaire will be able to post far larger totals in the coming months if he continues to actively urge his backers to give.

Aides said the pace of donations has continued in July and they believe Trump could build the kind of online fundraising juggernaut that drove Sen. Bernie Sanders's Democratic nomination bid.

“We’re extremely pleased with the response,” said Steven Mnuchin, Trump’s national finance chairman, noting the campaign just kicked off its online fundraising efforts two and half weeks ago. “We are seeing similar levels to the level of success that Bernie Sanders was able to attract from his supporters.”

The Trump campaign is hoping to draw some of the senator's supporters to back the Republican in the general election over Clinton.

“I think that this reflects the wide level of support and interest there is out there to see Donald Trump as president,” Mnuchin added.

Trump also contributed $3.8 million personally last month, bringing the total donations for the month to $55 million, the campaign said.

Both Donald Trump and Hillary Clinton are seeking six-figure checks from individual donors for their respective White House bids and down-ballot candidates. Here's how that works. (Sarah Parnass/The Washington Post)

It is unclear how much of the $51 million contributed by others will go directly to Trump’s campaign. More than $31 million was raised through two joint fundraising efforts with the RNC, which gets a share of the proceeds.

The Trump campaign must file a detailed report about its June fundraising and expenditures to the Federal Election Commission by July 20, which falls right in the middle of the Republican National Convention.

The campaign began its first real attempt to raise funds online in late June, after its most recent FEC filing showed it brought in just $5.4 million in May, including a $2.2 million loan from the candidate. That paltry total — and the fact that Trump began June with just $1.3 million in the bank —  astonished party leaders and fundraisers. They warned that the candidate’s fundraising deficit could hurt down-ticket Republicans counting on a well-funded RNC get-out-the-vote operation.

Trump responded to the criticism by first blaming party leaders for failing to rally around his candidacy and threatening to self-fund his bid, leaving the GOP to fend for itself.

But within days, his campaign began rolling out a series of emails asking supporters for donations. And the real-estate tycoon announced he was converting $50 million worth of loans he made to his campaign into donations, seeking to assuage fears he would use donations to pay himself back.

The billionaire, who spent much of the GOP primary lambasting the donor class, is now also actively seeking high-dollar contributions. He held 22 fundraising events in conjunction with the RNC since late May, bringing in $25 million. Party fundraisers are finalizing a busy schedule of coming finance events for Trump, who is set to headline several events nearly every week through the end of the summer, according to a person familiar with the plans.

It remains to be seen whether the real-estate tycoon can come close to matching Clinton’s fundraising totals — or whether he will need to. Trump has repeatedly scoffed at suggestions that he needs to adopt traditional political strategies, such as running costly television ads.

By the end of June, Clinton had raised about $288 million directly for her campaign and had more than $44 million in the bank. Trump appears to have brought in about $90 million during the same period, including $50 million of his own money. His campaign did not say how much it had on hand going into July.