Sheldon and Miriam Adelson were the biggest donors of the 2012 elections, but until August had not given a seven-figure check in this cycle.

GOP mega-donor Sheldon Adelson helped fill a fundraising shortfall for the host committee of the Republican National Convention, contributing $1.5 million toward financing the festivities in Cleveland, a new financial disclosure shows.

But the Las Vegas Sands chief executive gave far less than the $6 million the committee requested and did not give the money until Aug. 24, more than a month after the convention. The support for the convention came as he and his wife finally began writing a slew of big political checks, donating at least $20 million in super PAC money to bolster Republicans in congressional races.

Adelson and his wife, Miriam, a physician, topped the mega-donor charts in the 2012 campaign cycle, with nearly $93 million in disclosed contributions. But until August, they had not made any disclosed donations to groups that can accept unlimited amounts, despite Sheldon Adelson's reported promise to spend up to $100 million to bolster GOP presidential nominee Donald Trump.

The Cleveland host committee, which was tasked with raising $64 million to put on the events surrounding the convention, turned to the Adelsons for help after it had raised only $58.25 million by mid-July.

The host committee staff sent an urgent letter to the couple asking if they would consider giving $6 million to make up a shortfall caused by Trump's controversial candidacy. “Over the past couple months, negative publicity around our potential nominee resulted in a considerable number of pledges backing out from their commitments,” the letter said.

David Gilbert, chief executive of the Cleveland 2016 Host Committee, later said in a statement that the letter overstated how many pledges had been withdrawn in reaction to Trump. "It mischaracterized certain donations from individuals and corporations," he said. "Some of what were referred to as pledges were actually expectations based on pledges made to previous conventions, while a handful had been withdrawn from the host committee for 2016 Republican National Convention."

He added that despite a campaign to pressure corporations to drop their sponsorship of the RNC, the committee's fundraising had been "highly successful," saying it raised more money -- and at a faster pace -- than the past two RNC host committees.

In the end, the Cleveland host committee raised more than $65 million in cash and in-kind donations, a new Federal Election Commission filing shows. Major sponsors included AT&T (nearly $4.3 million), Microsoft ($1.8 million in software), Jones Day ($1.5 million) and oil interests such as Marathon Petroleum ($1.2 million). The Mercer Family Foundation, run by GOP mega-donor Rebekah Mercer, gave $500,000.

The Adelsons made their support for Trump official during the convention, posing for a photo with him. Their political adviser, Andy Abboud, tweeted the photo with the caption, "The Adelson's [sic] with their choice for President!"

It remains to be seen whether the couple has donated large sums to one of the super PACs backing Trump. Financial reports that cover August donations must be reported to the Federal Election Commission by midnight Tuesday.

Their support could complicate Trump's critique of wealthy donors and their influence on politics, a central plank of his campaign. After meeting with Sheldon Adelson in December during the GOP primaries, the real estate developer told The Washington Post, "I don’t want his money."

Anu Narayanswamy contributed to this report.