'The whole thing is a hoax. Everybody knows it,' Trump says
House Democrats are due to move forward this week with their case to make the real estate mogul only the third president ever to be impeached.
The House Judiciary Committee will hold a hearing on Wednesday at which experts will weigh whether Trump's alleged wrongdoing in pressuring Ukraine to investigate domestic political foe Joe Biden meet the constitutional bar for impeachment.
"The Democrats, the radical-left Democrats, the do-nothing Democrats, decided when I'm going to Nato -- this was set up a year ago -- that when I'm going to Nato, that was the exact time," Trump said angrily on departing the White House.
"It's an absolute disgrace what they're doing to our country," he said before his plane touched down in London.
"The whole thing is a hoax. Everybody knows it."
Trump's chief White House lawyer, Pat Cipollone, told the Democratic leader of the Judiciary Committee, Jerry Nadler, on Sunday that he was rejecting an invitation to send representatives to the session.
"We cannot fairly be expected to participate... while it remains unclear whether the Judiciary Committee will afford the President a fair process through additional hearings," Cipollone wrote.
Cipollone did not rule out White House participation in subsequent hearings. Throughout the drama, however, Trump has opted for stone-walling and flat-out resistance to what his supporters say amounts to a "coup."
Nadler told the White House on Monday that if "there is nothing to hide," then Trump should cooperate and "provide any exculpatory information that refutes the overwhelming evidence of his abuse of power."
Trump touts Zelensky interview
Trump got a boost Monday from an interview in which Ukrainian President Volodymyr Zelensky insisted he had not come under pressure from Trump.
The US president is accused of brazenly holding up hundreds of millions of dollars of military aid to Ukraine to force Zelensky to announce a politically embarrassing probe into Biden, one of the lead Democrats challenging Trump for the presidency in 2020.
A stream of high-level diplomats and several White House officials have testified in Congress about Trump's back-channel communications with Zelensky.
But Zelensky said Monday that he'd not been forced into anything.
"I did not speak with US President Trump in those terms: 'you give me this, I give you that,'" Zelensky said in an interview with several publications, including Germany's Der Spiegel magazine.
Trump says he was right to raise his concerns over alleged corruption by Biden and his son Hunter, who was controversially named to the board of a Ukrainian energy company accused of corrupt practices.
And he repeatedly echoed the Zelensky interview on Monday, saying "the Ukrainian president came out and said very strongly that President Trump did absolutely nothing wrong."
"That should be case over," Trump said.
GOP strikes back
Democratic lawmakers say that Zelensky, a neophyte politician facing armed conflict with Russia, was desperate to please Trump from the outset and remains unable to speak his mind for fear of losing support.
The House Intelligence Committee and its Democratic leader Adam Schiff has led the impeachment charge from the start.
The committee is expected to approve its investigation report on Tuesday in a closed-door vote set for 6pm (2300 GMT).
Trump's Republican backers on the intelligence committee on Monday released a 110-page rebuttal of the Democrats's case.
"The evidence does not establish any impeachable offense," it said.
Shortly after landing in Britain, Trump tweeted: "Great job! Radical Left has NO CASE."
Top Trump officials claim immunity
The House Judiciary Committee is expected to consider at least four articles of impeachment, including abuse of power, bribery, contempt of Congress and obstruction of justice.
A full vote in the Democratic-led House is currently expected before Christmas, before a trial next year in the Republican-dominated Senate -- where acquittal is seen as all-but-assured.
Democrats say they want to hear from former national security adviser John Bolton, acting White House chief of staff Mick Mulvaney and Secretary of State Mike Pompeo. All three are believed to have direct knowledge of Trump's actions toward Ukraine.
So far they have refused to testify, claiming "absolute immunity" as confidants of the president.
But as the Judiciary Committee hearings unfold, the White House may yet decide to send representatives to get their message across in what will likely be combative and at times raucous live television events.
"We'll see where the process goes," senior Trump adviser Kellyanne Conway said on Fox News.
She said the Democrats were inventing the entire scandal because "they have no idea how to beat him in 2020. They fear he will be re-elected."