Democrats have again raised the spectre of Donald Trump's impeachment as they asked a judge to unseal grand jury evidence relating to special counsel Robert Mueller's report.

In a major step forward in Democrats’ legal fight against the president, the House Judiciary Committee said it made the request to decide whether to recommend articles of impeachment.

“The US House of Representatives is the only institution that can now hold President Trump accountable for these actions,” the filing told Judge Beryl Howell, who oversaw Mr Mueller’s grand jury.

Most strikingly of all, the filing referenced the part of the US constitution that describes how Congress can impeach and remove a president from office - known as the Article I powers.

“The House must have access... to consider whether to exercise all its full Article I powers, including a constitutional power of the utmost gravity — approval of articles of impeachment,” the filing read.