Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, is demanding more information about the political opposition firm Fusion GPS, which compiled the controversial and partly unsubstantiated dossier on President Trump when he was a candidate last year.

Trump’s Republican and Democratic opponents reportedly paid the firm to do the opposition research against Trump during the campaign, and it contracted with British spy Christopher Steele to create the file, according to Grassley. Fusion GPS then shared the dossier with the FBI, which offered to pay Steele to continue the research on Trump, he said.