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CLEVELAND -- The organization tasked with raising money to mount the Republican National Convention has asked billionaire Republican donor Sheldon Adelson to fill a funding gap, NBC News has learned.

In a letter to Adelson, a Las Vegas casino magnate, the Cleveland Host Committee requested a $6 million after some corporate donors decided to stay away after the controversial Donald Trump won the GOP nominating contest. The committee has raised $58 million of its $64 million goal.

The letter was signed by CHC head David Gilbert.

“Your support will allow our community to meet its obligation to the RNC, and will ensure our Republican nominee has the best possible platform to lay out his conservative case for our nation,” the letter said, according to Politico.

Gilbert released a statement responding to the disclosure of the letter to Adelson.

"After initial discussions concerning a contribution, the staff of Mr. Sheldon Adelson requested specific information about the Host Committee’s fundraising at a very late hour and indicated a need for an immediate response," the Host Committee said.

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The leak of the letter is the latest evidence of the Trump effect on the convention. When NBC News interviewed Gilbert in March, more than a month before Trump clinched the nomination, the Host Committee had raised almost all the money necessary. Gilbert said he had raised $52 million, $7 million of which was an in-kind donation.

The letter also specifically named corporations or organizations that had not followed through on financial commitments, including a $1 million contribution from Koch Industries.

But a spokesperson for Koch, Ken Spain, said, "No commitment was made" to the Host Committee.

Gilbert addressed that issue as well.

"Unfortunately, this letter was not reviewed nor authorized by the Host Committee Chairpersons, and it mischaracterized certain donations from individuals and corporations," Gilbert said.

Adelson, who is estimated to be worth $25 billion, has been one of the Republican Party’s largest political donors. In the 2012 election, he and his wife Miriam gave more than $100 million to Republican candidates. But in this election year, he has yet to directly finance the 2016 election.

Sean Spicer, a communications director for the Republican National Committee, said he didn’t know about the letter to Adelson or the deficit.

On Wednesday in Cleveland, RNC finance chair Lew Eisenberg gave a report to Committee members that the RNC fundraising for the convention was strong.

Eisenberg said the RNC has raised $15.6 million for their convention fund.

The RNC’s convention fund is a separate organization from the CHC and raises money for separate functions at the convention.

The RNC and the host committee have a higher fundraising burden because Congress passes a measure in 2014 that no longer allows for federal funding of conventions, forcing parties to make up the difference.