The founders of Fusion GPS, the research firm behind the infamous Steele dossier, took aim at President Trump and his Republican supporters’ attempts to undermine the findings of the damning intel file in an op-ed published by The New York Times on Tuesday night. The dossier, a collection of intelligence reports on Trump’s links to Russia, has been portrayed by Trump’s Republican allies as unreliable and biased research that led to what they consider a witch hunt—the FBI’s Russia investigation. But Glenn Simpson and Peter Fritsch, the firm’s founders, say investigators had evidence of collusion long before their dossier was released. “As we told the Senate Judiciary Committee in August, our sources said the dossier was taken so seriously because it corroborated reports the bureau had received from other sources, including one inside the Trump camp,” Simpson and Fritsch wrote. They didn’t specify which source inside Trump’s camp they were referring to, but The New York Times reported last week that former Trump aide George Papadopoulos drunkenly told an Australian diplomat about Russia hacking the Democratic National Committee. Fusion GPS is urging Congress to release the full transcripts of their testimony. “The public still has much to learn about a man with the most troubling business past of any United States president,” they wrote.