Trump brushes off Parnas claims as Senate impeachment trial begins

"I don't know him at all. Don't know what he's about," Mr. Trump added.

But in interviews with MSNBC, CNN, and the New York Times, Parnas has said the President is not telling the truth about his efforts to put pressure on the leader of Ukraine.

Documents and electronic messages provided by Parnas to the House Intelligence Committee in recent days included a letter that Rudy Giuliani wrote in May 2019, asking for a meeting with the newly-elected Ukraine President, in which Giuliani said he was 'private counsel to President Donald J. Trump.'

"I don't know anything about the letter," President Trump said, praising Giuliani's time as mayor but not addressing what he did for Trump in Ukraine with Parnas and others.

Also denying any knowledge of Parnas's claims was Vice President Mike Pence.

"I don’t know the guy," Pence told reporters during a visit to Florida on Thursday, as the Vice President said the claim by Parnas that Pence knew about pressure being put on the Ukraine leader was 'completely false.'

Democrats used those denials to question why Pence's office has refused to declassify further impeachment answers from a State Department official detailed to his office.

Some Democrats have raised the possibility of asking to hear testimony from Parnas in the Trump impeachment trial, though any request for witness testimony must get a majority of Senators.

As of now, most Republicans remain hotly opposed to any new witnesses, arguing the Senate should not have to find evidence which the House did not uncover.

"That's not our job," said Sen. David Perdue (R-GA). "Our job is to look at what they brought us and decide if that rises to the level of impeachment."

Perdue was part of the ceremonial first day of the Senate impeachment trial - just the third time a President has faced such a challenge in U.S. history.

Opening arguments will take place next Tuesday.