Story highlights Schiller was around for some of the most controversial moments of Trump's political career

Comey's firing is now a key part of Justice Department special counsel Robert Mueller's investigation

Washington (CNN) Keith Schiller, one of President Donald Trump's closest confidants and longtime associates, denied on Tuesday to congressional Russia investigators the salacious claims about Trump's 2013 trip to Moscow that appeared in the opposition research Russia dossier about Trump, sources familiar with the matter told CNN.

Schiller, who quit his White House job in September, appeared for a closed-door interview to the House intelligence committee on Tuesday. He was by Trump's side for many years, including the trip to Moscow, but Schiller said little to the committee about past events involving Trump, according to the sources, telling lawmakers repeatedly that he could not recall or was not aware a number of potential Russia connections with Trump associates, which Democrats continually asked about.

Trump's activities while in Moscow for that event have been the subject of rampant speculation ever since the January leak of a 35-page dossier written by former British spy Christopher Steele. The dossier also accuses the Trump campaign of colluding with Russia as part of its active measures campaign to influence the election and defeat Democratic nominee Hillary Clinton.

Several of the dossier's most salacious claims have not been independently corroborated, and Schiller denied them on Tuesday.

The hearing with Schiller provided an opportunity for lawmakers to try to learn more about the Trump campaign's contacts with Russians and Trump's links to Kremlin-friendly interests in his business career.

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