Sens. Chuck Grassley Charles (Chuck) Ernest GrassleyGOP set to release controversial Biden report McConnell locks down key GOP votes in Supreme Court fight Senate Republicans face tough decision on replacing Ginsburg MORE (R-Iowa) and Lindsey Graham Lindsey Olin GrahamMcConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-S.C.) are pushing for information about Democrats' past work with the former British intelligence agent behind a controversial opposition research dossier about President 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's ties to Russia.

In a batch of letters sent Thursday, Grassley and Graham asked former Democratic National Committee (DNC) and 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 campaign officials to turn over information regarding potential interactions with the agent, Christopher Steele, who was retained by Fusion GPS during the 2016 presidential campaign to conduct research on Trump.

The letters were sent as part of a Senate Judiciary Committee investigation into the FBI's interactions with Steele and the extent to which the FBI may have relied on the controversial dossier to obtain authorization to surveil individuals associated with Trump's campaign.

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The letters were sent to DNC Chairman Tom Perez Thomas Edward PerezClinton’s top five vice presidential picks Government social programs: Triumph of hope over evidence Labor’s 'wasteful spending and mismanagement” at Workers’ Comp MORE, Clinton's campaign, former DNC Chairwoman Rep. Debbie Wasserman Schultz Deborah (Debbie) Wasserman SchultzFlorida Democrat introduces bill to recognize Puerto Rico statehood referendum Five things to watch at the Democratic National Convention Michelle Obama wishes Barack a happy birthday: 'My favorite guy' MORE (R-Fla.), former interim DNC Chairwoman Donna Brazile, former Clinton campaign chairman John Podesta and former Clinton campaign chief strategist Joel Benenson.

The Washington Post reported last year that the dossier compiled by Steele, which contains salacious and unverified allegations against Trump, was funded in part by a law firm retained by the Clinton campaign.

It was later revealed that the conservative Washington Free Beacon initially retained Fusion GPS's services to conduct research into Trump, though it stopped funding the research before Steele was hired by the firm.

Since then, some Republicans have questioned the extent to which the FBI relied on the dossier as part of its investigation into Russian meddling in the 2016 election and possible ties between the Trump campaign and Moscow.

Fusion GPS has defended the document Steele produced, saying he was not made aware of who was funding the research.

Grassley and Graham have been particularly critical of the dossier. Earlier this month, the two GOP senators referred Steele to the Justice Department for possible criminal prosecution for making what they said were "potentially false statements about the distribution of claims from the dossier."