In a series of increasingly angry tweets Mr Trump said congressional testimony from inquiry witnesses should not be released publicly.
“If Shifty Adam Schiff, who is a corrupt politician who fraudulently made up what I said on the ‘call’, is allowed to release transcripts of the Never Trumpers [and] others that are [and] were interviewed, he will change the words that were said to suit the Dems purposes,” he wrote on Sunday evening.
In an extraordinary claim, the 73-year-old alleged that Mr Schiff, who chairs the House Intelligence Committee, could manipulate witness transcripts.
“Republicans must have nothing to do with Shifty’s rendition of those interviews,” Mr Trump added
“He is a proven liar, leaker & freak who is really the one who should be impeached!”
House Democrats voted last week to authorise Mr Schiff to lead the public inquiry. This will include hearings in which witnesses are questioned.
The congressman’s remit is a broad one but will focus on the president’s alleged behaviour during the Ukraine call.
The president has repeatedly denied offering a quid pro quo.
Alexander Windman, one of the witnesses and previously the National Security Council director for Ukraine, told Congress last week that he approached White House lawyers after the call because its contents had left him so concerned.
John Eisenberg, deputy counsel to the president for national security affairs, later told Mr Windman not to tell anyone about the phone call.
Mr Trump has regularly attacked Adam Schiff in the past. The president called the congressman “Shifty Adam Schiff” for the first time on Twitter in April 2019.
He has also previously implied, without evidence, that Mr Schiff is corrupt, guilty of fraud and leaks to the media.
Jesse Waters, another Fox presenter, also accused Mr Schiff of being “totally corrupt” last month.
Brian Klaas, an assistant professor in global politics at UCL, criticised the president’s social media conduct.
“Trump calls the chairman of the House Intelligence Committee “a freak” and invents yet another insane conspiracy theory and it will barely be a story,” he said, on Twitter.
“Democracy erodes when previously unthinkable conduct becomes so routine that it’s barely even noticed by voters.”
The Ukraine scandal began when a whistleblower, thought to be a member of the intelligence community, reported the president’s behaviour.
On Sunday, the president urged journalists to publicly identify the whistelblower.
“You would be doing the public a service if you did,” the president claimed.
He also refused to rule out shutting down the government if Democrats did not stop the impeachment inquiry.
“We’ll see what happens,” the 73-year-old said. “I wouldn’t commit to anything.”
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