Justice Department official Bruce Ohr is scheduled to testify behind closed doors before Congress on Tuesday about his alleged ties to the infamous Trump dossier and the DOJ's knowledge of the salacious allegations about President Trump's ties to Russia.

Republican lawmakers have alleged that Ohr played a pivotal role in selling the unverified dossier, created by Fusion GPS – where his wife Nellie Ohr worked – and paid for by Hillary Clinton's campaign and the Democratic National Committee.

The dossier was used by federal officials to justify the surveillance of a top Trump aide, Carter Page.

On "Fox & Friends," Rep. Ron DeSantis (R-Fla.), a member of the House Oversight Committee, said he wants to know Ohr's "precise role" in relation to the dossier.

Gaetz: The Ohrs Were the 'Bonnie and Clyde of Collusion', Manafort Case Unimportant

Levin on Indictment or Impeachment: Trump in 'Great Shape' Under the Law

"We know just from the documents that we have that he was functioning almost as an intermediary between the Clinton campaign and Fusion GPS and the Obama Justice Department," DeSantis said.

He said that it was an "unprecedented" use of official prosecutorial resources for Ohr apparently to be involved in generating opposition research on the Trump campaign.

He said Ohr is a critical player in the Russia collusion allegations, and there are a host of questions lawmakers want to ask him.

"We need to know who else at the FBI knew what he was doing, we need to know when he started dealing with people like Glenn Simpson at Fusion GPS, what his interactions were with Christopher Steele, and the financial interests he had at stake," DeSantis said.

Watch more from "Fox & Friends" above.

Rep. Issa: Bruce & Nellie Ohr Should Admit They Were Part of 'Conspiracy' Against Trump

Dershowitz: 'Greatest Risk' to Trump Is From NY Prosecutors, Not Mueller Probe