Democratic lawmakers on Friday demanded that the White House turn over documents related to allegations that President Donald Trump pressured Ukraine for political favours, as the explosive impeachment investigation against the US leader intensified.
The congressional committees leading the probe cranked up the heat on the White House as evidence mounted that Trump illicitly used his office to enlist Ukraine's President Volodymyr Zelensky's help to damage 2020 Democratic rival Joe Biden in exchange for military aid.
"The White House has refused to engage with - or even respond to - multiple requests for documents from our Committees on a voluntary basis. After nearly a month of stonewalling, it appears clear that the President has chosen the path of defiance, obstruction, and cover-up," the Democratic chairmen of the House oversight, intelligence and foreign affairs committees said in a statement.
"We deeply regret that President Trump has put us - and the nation - in this position, but his actions have left us with no choice but to issue this subpoena."
The committees sent a letter to acting White House Chief of Staff Mick Mulvaney, demanding that he turn over the requested files by October 18.
The subpoena followed a broad demand earlier Friday for documents from Vice President Mike Pence.
The investigators pointed to Mr Pence's knowledge of Mr Trump's calls to Mr Zelensky and his own meeting on September 1 with the Ukraine leader, as well as discussions he may have made with Mr Trump and US diplomats about Ukraine and obtaining political dirt on Mr Biden.
A series of text messages between US diplomats dealing with Ukraine supported Democratic accusations that Trump had illegally sought foreign help for his re-election effort.
And the Wall Street Journal reported that, in an interview, Republican Senator Ron Johnson said he had learned that a quid pro quo had been proposed to Zelensky's government by Mr Trump's emissaries, tying military aid to a Ukraine corruption investigation into Biden.
Mr Trump pushed back hard, saying there was no quid pro quo and, in an effort to recast the entire saga, insisted it was his responsibility to investigate "corruption."
"I don't care about Biden's campaign but I care about corruption," he told reporters.
"I don't care about politics," he said. "I believe there was tremendous corruption with Biden."
The democratic presidential candidate responded by saying Mr Trump was himself corrupt and was trying to intervene in the Democrats' process for choosing a presidential candidate, a race that Mr Biden currently leads.
Mr Trump is "the most corrupt president we've had in modern history," Mr Biden said at a campaign event in Los Angeles.
"I am not going to stand for it," the candidate said, calling Mr Trump "unhinged."
"He has indicted himself by his own statements," Mr Biden said, one day after the president openly called for both Beijing and Kiev to investigate the former vice president for corruption.
Mr Trump has alleged that Joe Biden's son Hunter earned "millions" from a business association in which he sat on the board of directors of a Ukraine tycoon's gas company.
But no evidence has surfaced showing any wrongdoing on the part of either Mr Biden, and the diplomats' text messages showed that some had doubts about Mr Trump's pressure on Mr Zelensky, including by temporarily freezing a $400 million aid package, for help in Mr Trump's "domestic, re-election politics," as one wrote.
Also on Friday, Democrats interviewed Michael Atkinson, the intelligence community's inspector general, who handled the anonymous whistleblower complaint about Mr Trump's Ukraine dealings that broke open the scandal two weeks ago.
The release last week of the complaint and a summary of Mr Trump's July 25 call with Mr Zelensky, in which he asked for a "favour" and referred to investigating Mr Biden ignited the Democrats' impeachment inquiry.
Adam Schiff, chairman of the House Intelligence Committee, said Mr Atkinson's testimony offered further justification to his decision to label the whistleblower's complaint urgent and credible.
The July 25 call record "shows that Trump pressured a foreign leader to interfere in the 2020 election by investigating a political opponent. Those facts cannot be seriously contested," Mr Schiff said.
As Democrats raised their attacks on the president, many Republicans remained muted, supportive of Mr Trump but keeping a distance.
Breaking with the pack, Republican Senator Mitt Romney blasted Mr Trump's comments that Beijing and Kiev should investigate Mr Biden for corruption.
"By all appearances, the President's brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling," tweeted Mr Romney, the Republican presidential nominee in 2012.
"When the only American citizen President Trump singles out for China's investigation is his political opponent in the midst of the Democratic nomination process, it strains credulity to suggest that it is anything other than politically motivated."
Joe Biden's campaign called Mr Trump's comments already-debunked "conspiracy theories" and accused Mr Trump of "a grotesque choice of lies over truth and self over the country."
"Mr. President, you cannot extort foreign governments to help you win re-election. It's an abuse of power. It violates your oath of office. And it jeopardises our national security," Mr Biden tweeted separately.