A US House committee is taking legal action to access the grand jury evidence gathered by Robert Mueller during his investigation of the Trump campaign.
US House Judiciary Committee Chairman Jerrold Nadler says he will go to court to seek access to grand jury evidence compiled by former Special Counsel Robert Mueller's 22-month probe of Russian meddling in the 2016 presidential election.
Mr Nadler told a news conference on Friday that since Justice Department policy does not allow the prosecution of a sitting president, the US House of Representatives is the only institution of government that could hold President Donald Trump accountable for actions outlined in the Mueller report.
"To do so, the House must have access to all the relevant facts and consider whether to exercise its full ... powers, including a constitutional power of the utmost gravity, recommendation of articles of impeachment," Mr Nadler said, reading from the court petition.
A second pending legal move by Democrats, a federal lawsuit to compel testimony from former White House counsel Don McGahn about Mr Trump's efforts to impede the Russia probe, will come early next week, Mr Nadler told the news conference.
Mr McGahn, a star witness in the 448-page Mueller report released in April, told federal investigators that Mr Trump directed him to seek Mr Mueller's removal and then to deny that he had been instructed to do so.
Democrats view the alleged episode as an act of obstruction of justice that could lead to impeachment proceedings against the Republican president.
Mr Nadler said the grand jury information gathered during Mr Mueller's investigation "is critically important for our ability to examine witnesses, including former White House counsel Don McGahn, and to investigate the president's misconduct.
"We will win the court fight because the legal excuses the White House has been using are extraordinarily weak from a legal point of view," Mr Nadler told CNN earlier in the day.
The top Republican on the Judiciary Committee, Doug Collins, criticised Mr Nadler's move.
"Judiciary Democrats are suing for grand jury material to which they have no right. ... Chairman Nadler's legal action here is sure to fail, weakening congress's ability to conduct oversight now and into the future," Mr Collins said in a statement.
Mr Nadler described the pending legal actions, particularly the McGahn lawsuit, as a potential watershed that could dismantle recent White House efforts to stonewall congressional investigators by directing current and former Trump aides to defy subpoenas and refrain from providing testimony.
"It will open up the floodgates to all, to enforce all the subpoenas and get all the testimonies because they're all the same nonsense legal argument," he said.
Mr Mueller testified in congress on Wednesday in back-to-back hearings that Democrats hoped would focus public attention on Mr Trump's alleged misconduct and boost support for an impeachment inquiry.
But his halting and reticent performance changed few opinions, leaving House Democrats to accelerate a congressional probe that could take months to bear fruit.
House Speaker Nancy Pelosi, who opposes impeachment for now as a politically risky move for Democrats, told reporters that she favoured litigation to obtain "the best, strongest possible case" against Trump.
Mr Mueller found insufficient evidence to allege that the Mr Trump campaign conspired with Moscow in its effort to help Mr Trump get elected in 2016, although campaign officials met with Russians.
He also reached no conclusions on whether Mr Trump tried to obstruct Mr Mueller's inquiry.
But Democrats say that testimony from Mr McGahn about Mr Trump's efforts to remove Mr Mueller could give them the evidence they need for an impeachment inquiry.
Mr McGahn declined to testify earlier this year after the White House directed him not to co-operate with the committee.