Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE ally David Brock has issued a provocative challenge to Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE: Release your tax returns, and a major Republican donor will donate $5 million to a veterans charity of Trump's choosing.

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Brock has yet to reveal the identity of the Republican donor, who he says has pledged the money on the condition that Trump, the presumptive GOP presidential nominee, releases his tax returns by a certain date.

An associate of Brock's, Erin Bzymek, said Brock would reveal the details of the GOP donor challenge in a conference call with reporters Wednesday morning.

"The effort represents an opportunity to fill in some of the unknowns about Trump including how much he has made off of potentially fraudulent ventures and how much he’s actually paid in taxes," Bzymet said in a statement Tuesday afternoon.

"Brock will speak on the call about the details of the $5 million challenge that sets a hard deadline for Trump to release his tax returns."

Brock is a controversial figure who delights in playing hardball politics. He runs the pro-Clinton super-PAC Correct the Record along with a number of other progressive and Clinton-aligned groups.

The Hill has asked the Trump campaign whether he will accept the challenge.