The Georgia Democratic congressman said in an interview Friday he didn't view Trump as a "legitimate president" amid reports that Russian cyberattacks had intended to influence the elections.
Critics have long raised concerns about Gen. Michael Flynn's relationship with Moscow. The nominee for national security adviser was in regular contact in December with Russia's ambassador to the U.S.
The dossier lists unverified allegations about Donald Trump, claiming Russia has evidence as blackmail material. News outlets have identified former MI6 officer Christopher Steele as the author.
In his first news conference since last summer, he denied unverified reports that Russia has compromising intelligence on him and outlined how he'd try to unwind his complex businesses as president.
The Kremlin denied that it collects political dirt, known as kompromat. But disinformation, fake photos and leaked sex tapes have long been features of Russian politics.
Intelligence officials recently briefed both Obama and Trump about the unconfirmed reports. U.S. intelligence agencies have said Russia engaged in an extensive hacking effort during the 2016 election.
The FBI director, appearing with other top U.S. intelligence chiefs at a Senate Intelligence Committee hearing, said Russia targeted Republican National Committee Web domains no longer in use.
The public version of the intelligence report on the investigation into Russia's interference in the U.S. elections concludes that Russia "aspired to help" Trump's election chances when possible.
When the Soviet Union came crashing down 25 years ago, many Russians hoped their country would become a democracy. But increasingly, government critics are choosing political exile.