The co-founder of the firm who ordered a salacious dossier on President Trump will testify before the Senate Judiciary Committee next week.

Glenn Simpson’s opposition research firm, Fusion GPS, hired former British spy Christopher Steele to investigate then-candidate Trump.

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The dossier produced by Steele claims Trump and the Kremlin had worked together to undermine Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE’s campaign.

The unsubstantiated findings in the dossier were released to media outlets and published by BuzzFeed in January.

Simpson will testify before the committee on Wednesday.

Senate Judiciary Chairman Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE (R-Iowa) demanded details on the dossier in a letter last May, and threatened to subpoena Fusion GPS in June.