In the first legal submissions of President Donald Trump's impeachment trial, Democrats on Saturday said the President had violated his oath and should be removed from office, while the White House denounced the impeachment charges of abuse of power and obstruction of Congress as 'constitutionally invalid.'

In their 111 page legal brief, Democrats said the President had abused his power by trying to pressure the government of Ukraine into announcing investigations against Joe Biden, all in an effort to help Mr. Trump's 2020 re-election bid.

Democrats said the very public effort by President Trump to block top White House officials from testifying before Congress - as they defied subpoenas for the impeachment investigation - was a violation of the Constitution.

"In exercising its responsibility to investigate and consider the impeachment of a President of the United States, the House is constitutionally entitled to the relevant information from the Executive Branch concerning the President's misconduct," Democrats wrote.

"The Framers, the courts, and past Presidents have recognized that honoring Congress’s right to information in an impeachment investigation is a critical safeguard in our system of divided powers," that trial brief added.

In their initial answer to the Senate summons for this impeachment trial, the White House delivered a seven page legal rebuke to Democrats.

"The Articles of Impeachment are constitutionally invalid on their face. They fail to allege any crime of violation of law whatsoever," wrote White House Counsel Pat Cipollone and the President's personal lawyer Jay Sekulow.

"In the end, this entire process is nothing more than a dangerous attack on the American people themselves and their fundamental right to vote," the President's legal team concluded.

"The notion that President Trump obstructed Congress is absurd," said sources close to the President's legal team.

The White House has until 12 noon on Monday to file a trial brief to the Senate; Democrats would have until 12 noon on Tuesday to file a rebuttal.

The Senate will reconvene as a court of impeachment on Tuesday afternoon. Senators must still approve rules to govern the first phase of the trial.

Senate Republicans have said they would base that rules plan on one approved by the Senate for the start of the Clinton impeachment trial in 1999.

That rules resolution gave each side 24 hours to make their opening arguments - which would likely be split up over three or more days on the Senate floor.

Like 1999, it's possible the Senate may also take an early vote to dismiss the case entirely, an outcome preferred by President Trump.