Transcript for Trump has upset possible key witness for special counsel's Russia investigation: Source
When it comes to the Russia investigation, the trump campaign adviser who pleaded guilty to lying to the FBI, we're learning his explanation for lying. Here's Brian Ross. Reporter: This campaign picture, and Donald Trump's own words left no doubt that George papadopoulos was part of the trump foreign policy team, the table for this meeting. George papadopoulos, excellent guy. Reporter: But once papadopoulos pleaded guilty to lying to the FBI about his contacts with Russia, it was a different story from the president. I don't remember much about that meeting, it was a very unimportant meeting. Took place a long time. Don't remember much about it. Reporter: A presidential tweet called papadopoulos a low level volunteer. What papadopoulos did was lie, and that's on him, not on the campaign. Reporter: Now, a person with direct knowledge of the Russia investigation, says the president's words have upset George papadopoulos. That he was only trying to be loyal to Donald Trump when he lied to the FBI, not wanting to contradict what the president had already said about campaign contacts with Russia. It's all fake news. It's phony stuff. It didn't happen. Reporter: Papadopoulos tried to stick to the official line, telling FBI agents, that his contacts with Russia "Occurred before" he joined the trump campaign. That was not true. It was only after he joined the campaign that he was contacted by Russians, offering "Dirt" on Hillary Clinton and tried to arrange meetings between trump and Russian president Putin. Democrats say the president's effort to distance himself from papadopoulos raises its own questions. You're a senior foreign policy adviser until you do something that exposes the connections of the campaign. Brian, important to point out that George papadopoulos not only pleaded guilty to lying but now cooperating with Robert Mueller. Clear the comments are not sitting well with him and he is poisoned to be a key witness in this investigation. Brian, thank you. Next this evening we turn to the new video and the very close
This transcript has been automatically generated and may not be 100% accurate.