US President Donald Trump lashed out at Democrats for continuing with hearings in the impeachment inquiry while he heads to London to meet with leaders of NATO member states to mark the alliance's 70th anniversary.
"It's an absolute disgrace what they are doing to our country," Trump said as he prepared to depart Washington for London, noting the NATO meeting was planned well in advance.
The president said he would not be sending lawyers to impeachment inquiry hearings, calling the process a "hoax".
Shortly after he was wheels up for the approximately seven-hour flight, Trump took to Twitter to bash the opposition party once more.
"Heading to Europe to represent our Country and fight hard for the American People while the Do Nothing Democrats purposely scheduled an Impeachment Hoax hearing on the same date as NATO. Not nice!" he said, accompanied by a video of Air Force One taking off.
The president has latched on to an interview by Ukrainian President Volodymyr Zelenskiy with the German news magazine Der Spiegel in which he denied that there had been a quid pro quo deal with Trump.
"I definitely did not speak with US President Trump in such a way, like, 'you give me this, I give you that,'" Zelenskiy said.
Democrats have discounted remarks coming from Kiev, in part noting that the country remains dependent on US assistance.
Trump has vowed to raise the issue of NATO members' defence spending during the leaders' meeting. "They are going to have to do a little more burden sharing," he said, insisting that the status quo has been "unfair" to the US.
Trump has been pressuring NATO members to meet their defence spending target of 2 per cent of GDP, as the states agreed during a summit in 2014. Most members fall short of their stated goal, and the alliance remains heavily reliant on the US.
At the same time, the president has on occasion sounded less than fully committed to the trans-Atlantic alliance and the mutual defence framework at the heart of NATO, worrying key European allies. The quasi-withdrawal of US troops from Syria has added to concerns.
On Wednesday, as Trump is due to wrap up his trip to London and will likely hold a press conference, the judiciary committee at the House of Representatives will start the second phase of the impeachment inquiry.
The Democrats, who control the House, launched the impeachment inquiry in September, accusing the president of abusing the power of his office to pressure Ukraine to investigate his domestic rival, Joe Biden, the Democratic Party's frontrunner for the 2020 nomination.
The second phase of the inquiry will focus on the legal basis for drawing up articles of impeachment.
The first phase, at the intelligence committee, was a fact-finding mission that included public hearings where several witnesses testified they were concerned about the White House's relationship with Ukraine and the possible leveraging of military aid to get dirt on Biden.
Trump's media adviser, Kellyanne Conway, went on Fox News to accuse the Democrats of seeking to impeach the president from the moment he took office in 2017.
"They should just admit they have no idea how to beat him in 2020," she said. "They fear he will be re-elected."
While Trump has struggled with his approval ratings for nearly three years, his path to another four years in the White House remains open, with 11 months to go until the US holds the vote.