Donald Trump has urged Republicans to get tough and fight for his presidency, saying the Democratic-led US House of Representatives wants to impeach him "as quick as possible" over his request that Ukraine investigate a political rival.
Trump made his comments during a White House Cabinet meeting as Democrats sought to build public support for their fast-moving impeachment inquiry and the administration pressed its efforts to stonewall the probe.
House Speaker Nancy Pelosi issued a video and "fact sheet" that may give hints about the articles of impeachment - formal charges - Democrats may pursue against Republican Trump, accusing him of abuse of power, a "shakedown" involving Ukraine and a cover-up.
Republicans in the House of Representatives tried to censure one of the inquiry's leaders, House Intelligence Committee Chairman Adam Schiff, but the motion was blocked by Democrats who control the chamber.
Few Republican lawmakers have shown an inclination to remove Trump from office even as Democrats focus on his pushing a vulnerable foreign ally to interfere to his benefit in the November 2020 US election by providing political dirt on Joe Biden, a leading Democratic contender to run against Trump.
Senator Mitt Romney is one of the few Republicans who have sharply criticised Trump, who has denied wrongdoing.
Other Republicans have expressed misgivings about Trump policies, including criticism from Senate Majority Leader Mitch McConnell and Senator Lindsey Graham of his withdrawal of US troops in northeastern Syria, which exposed US-allied Kurdish fighters to a Turkish cross-border offensive.
Approval of articles of impeachment in the House would prompt a trial in the Republican-led Senate on whether to remove Trump from office.
"The Republicans have to get tougher and fight. We have some that are great fighters, but they have to get tougher and fight, because the Democrats are trying to hurt the Republican Party before the election," Trump said.
Trump said the Democrats are "vicious and they stick together."
"They don't have Mitt Romney in their midst. They don't have people like that. They stick together," Trump added.
In an interview aired with "Axios on HBO," Romney denounced Trump's requests to Ukraine and China to investigate Biden, questioned Trump's character, criticised his decision to "abandon" Kurdish allies and deplored his hush money payment to an adult film star.
Romney was the 2012 Republican presidential nominee but lost to incumbent Barack Obama.
Asked if it is a foregone conclusion that House Democrats will vote to impeach him, Trump said: "They want to impeach. And they want to do it as quick as possible."
At the heart of the inquiry is a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to investigate Biden and his son Hunter, who had been a director of a Ukrainian energy company, as well as a discredited theory that Ukraine, and not Russia, interfered in the 2016 US election.
Another round of testimony in the inquiry is set for this week.
Acting White House budget director Russell Vought said both he and Michael Duffey, associate director for national security programs at the Office of Management and Budget, would not provide depositions to the committees leading the inquiry.
Duffey had been scheduled to testify behind closed doors on Wednesday as Democrats investigate whether Trump withheld $US391 million in security aid to Ukraine to pressure the country to investigate Biden and its own role in the US election.
Australian Associated Press