President Trump tore into Rep. Adam Schiff, D-Calif., in harsh terms on Tuesday, taking a moment from his overseas tour in London to call the House Intelligence Committee chairman a “maniac” and a “deranged human being” over his handling of the impeachment inquiry.

Trump was speaking to reporters alongside Canadian Prime Minister Justin Trudeau on the sidelines of a NATO summit, when he was asked what he would hope to learn from having Schiff testify in a possible Senate impeachment trial -- a scenario some Republicans would like to see.

HOUSE GOP REPORT SAYS NO EVIDENCE FOR TRUMP IMPEACMENT, WARNS OF 'DANGEROUS PRECEDENT'

“I learn nothing from Adam Schiff, I think he’s a maniac,” Trump said. “I think Adam Schiff is a deranged human being. I think he grew up with a complex for lots of reasons that are obvious. I think he’s a very sick man, and he lies.”

The comments demonstrated how the impeachment fight has followed Trump even as he meets with world leaders in London on issues ranging from defense spending to ISIS. Trump focused Tuesday on a controversial move by Schiff in September, where he read out a hyperbolic account of Trump’s controversial July 25 phone call with Ukrainian President Volodymyr Zelensky.

“I have a favor I want from you,” Schiff said in a hearing while appearing to read from a piece of paper. “And I’m going to say this only seven times, so you better listen good. I want you to make up dirt on my political opponent, understand? Lots of it, on this and on that.”

Schiff later chalked up his fictional summary of the phone call to a joke as he came under fire from conservatives for making up quotes.

“My summary of the president’s call was meant to be at least, part, in parody," Schiff said. "The fact that that’s not clear is a separate problem in and of itself. Of course, the president never said, ‘If you don’t understand me I’m going to say it seven more times.' My point is, that’s the message that the Ukraine president was receiving in not so many words."

Trump has repeatedly criticized Schiff for the move.

“This guy is sick,” he said on Tuesday. “If he didn’t do that in the halls of Congress, he’d be thrown in jail.”

Schiff has been pushing back against Trump, telling CNN last week that the case against Trump on Ukraine is "ironclad" and accused the White House of "stonewalling" the impeachment inquiry and related oversight by his committee.

Trump's remarks come a day before the first formal impeachment hearing in the House Judiciary Committee and as House Intelligence Committee Democrats are poised to vote on and release an impeachment report to send to the Judiciary panel. Democrats have alleged that the phone call between Trump and Zelensky was part of Trump’s effort to get a political investigation into former Vice President Joe Biden in exchange for military aid. Trump has denied that claim.

Earlier Tuesday, House Republicans wrote to Judiciary Committee Chairman Jerry Nadler, D-N.Y., accusing him of making bipartisan cooperation “the exception, rather than the rule.”

“Under your leadership, bipartisan solutions to real problems affecting real Americans have been sacrificed in favor of Committee Democrats’ obsession with impeaching the president and undoing the 2016 election,” the letter says.

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It marks part of a broader offensive push by Republicans, as some polls have shown that the impeachment hearings have not swung public opinion in favor of impeachment.

On Monday, House Republicans delivered a point-by-point rebuttal to Democrats’ impeachment efforts, claiming in their own minority report that the evidence collected in the inquiry to date does not support the accusations leveled against President Trump -- or rise to the level of removal from office.

Fox News' Mike Emanuel and Brooke Singman contributed to this report.