Special Counsel Robert Mueller's team has met with Tony Fabrizio, one of Donald Trump's campaign pollsters who is also a former business associate of former Trump campaign chairman Paul Manaforts, in February 2018.
The New York Times later reported that Manafort instructed Kilimnik to provide the data to Serhiy Lyovochkin and Rinat Akhmetov, two Ukrainian oligarchs who Manafort has worked for in the past.
"No, I didn't know anything about it", he told reporters at the White House.
That information was included in a court filing this week that appeared to inadvertently include details not meant to be made public and indicates a pathway by which the Russians could have had access to Trump campaign data.
"If accurate, this is damning evidence of a senior Trump campaign official providing information to individuals tied to Russian intelligence at the height of the Kremlin's effort to undermine our election", Warner said.
Mueller accused Manafort of lying to his prosecutors in late November and later said that the breaches came in five different areas, including his contacts with Kilimnik and the Trump administration.
Jackie Speier, a Democratic member of the House Intelligence Committee, said the revelations raised new questions about possible "collusion" between Trump's election team and Russian Federation.
U.S. District Court Judge Amy Berman Jackson ordered Mueller to respond by January 14 with "factual and evidentiary basis" for why it is accusing Manafort of lying during his cooperation.
Rudy Giuliani, a lawyer for Trump who has repeatedly criticized the Mueller probe as a fruitless "witch hunt", dismissed the sharing of data with Kilimnik as inconsequential.