Trump was impeached for abuse of power and obstruction of Congress. Trump denies any wrongdoing.

At the time of the call, Trump was withholding $391m in military aid from Ukraine.

The impeachmnent inquiry centred on a call between Trump and Ukraine's president in which Trump asks for a probe into the Bidens. Trump also wanted a probe into a conspiracy theory about the 2016 elections.

The United States Senate Majority Leader Mitch McConnell on Monday proposed a condensed, two-day calendar for each side to give opening statements in President Donald Trump's impeachment trial, ground rules that are raising objections from Democrats on the eve of the landmark proceedings.

The Republican leader outlined the process in a four-page resolution that will be voted on as one of the first orders of business when senators convene on Tuesday. It also pushes off any votes on witnesses until later in the process, rather than upfront, as Democrats demanded.

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McConnell has been angling for a speedy trial towards the acquittal of the charges against the president, and the closely held rules package arrived on Monday after Trump's legal team asserted in a legal brief that he did "absolutely nothing wrong", urging the Senate to swiftly reject the "flimsy" and rigged impeachment case against him.

With Republicans holding the Senate majority, McConnell's proposal is likely to be approved by senators in the president's party.

The Senate Democratic leader, Chuck Schumer, called the Republican leader's proposed rules package a "national disgrace".



"It's clear Senator McConnell is hell-bent on making it much more difficult to get witnesses and documents and intent on rushing the trial through," Schumer said. He promised to propose votes to try to amend the package.

White House welcomes resolution

The rules package arrived late on Monday as Capitol Hill was bracing for the start of the trial.

After the four days of opening statements - two days per side - senators will be allowed up to 16 hours for questions to the prosecution and defence, followed by four hours of debate. Only then will there be votes on calling other witnesses.

In the rare event that senators agree to call witnesses, the rules propose that any witness must be deposed and the Senate would then decide which ones, if any, would testify in public.

At the end of deliberations, the Senate would then vote on each impeachment article.

Trump waves before boarding Marine One on the South Lawn of the White House [Alex Brandon/AP Photo]

The White House welcomed the proposal for a speedy trial.

"We are gratified that the draft resolution protects the president's rights to a fair trial, and look forward to presenting a vigorous defence on the facts and the process as quickly as possible, and seeking an acquittal as swiftly as possible," said White House Legislative Affairs Director Eric Ueland.

In a brief from Trump's lawyers, they argued he did "absolutely nothing wrong" and urged the Senate to swiftly reject the "flimsy case".

"All of this is a dangerous perversion of the Constitution that the Senate should swiftly and roundly condemn," the lawyers wrote. "The articles should be rejected and the president should immediately be acquitted."

Demands for 'fair trial'

The 110-page brief from the White House, plus the House Democratic response, come as the Senate could be facing 12-hour sessions for the rare trial taking place in an election year, with some of the very senators running to replace Trump as president sitting as jurors. Democrats warned that such a plan would almost certainly push the proceedings into hours when Americans may not be watching.

With security tightening at the Capitol, the House prosecutors made their way through crowds of tourists in the Rotunda to tour the Senate chamber. The White House legal team led by Pat Cipollone and Jay Sekulow soon followed, both sides under instructions to keep the chamber doors closed to onlookers and the media. Four TV monitors were set up inside to show testimony, exhibits and potentially tweets or other social media, according to a person familiar with the matter but unauthorised to discuss it who spoke on condition of anonymity.

Senators are poised for only the third trial of its kind in US history, but first, they must contend with a rules fight and whether to allow new witnesses.

In their own filing Monday, House prosecutors issued fresh demands for a fair trial in the Senate.

"President Trump asserts that his impeachment is a partisan 'hoax.' He is wrong," the prosecutors wrote.

The House Democrats led by Chairman Adam Schiff of the Intelligence Committee said the president cannot have it both ways - rejecting the facts of the House case but also stonewalling congressional subpoenas for witnesses and testimony. "Senators must honour their own oaths by holding a fair trial with all relevant evidence," they wrote.

House Speaker Nancy Pelosi speaking during a news conference to announce impeachment managers on Capitol Hill in Washington [Susan Walsh/AP Photo]

The White House document released on Monday says the two articles of impeachment brought against the president - abuse of power and obstruction of Congress - do not amount to impeachable offences. It asserts that the impeachment inquiry centered on Trump's request that Ukraine's president opens an investigation into Democratic rival Joe Biden was never about finding the truth.

The impeachment case accuses Trump of abusing power by withholding military aid from Ukraine at the same time as he was seeking an investigation into Biden and obstructing Congress by instructing administration officials not to appear for testimony or provide documents, defying congressional subpoenas.

In a brief filed earlier, House Democrats called Trump's conduct the "worst nightmare" of the framers of the constitution.

"President Donald J Trump used his official powers to pressure a foreign government to interfere in a United States election for his personal political gain," the House prosecutors wrote, "and then attempted to cover up his scheme by obstructing Congress's investigation into his misconduct."

But Trump's team contended on Monday that even if Trump were to have abused his power in withholding the Ukraine military assistance, it would not be impeachable because it did not violate a specific criminal statute.

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The president's team issued several opinions from the Justice Department's Office of Legal Counsel to back up its claims and support its position that it had not illegally defied Congress.

While the Senate, with a 53-47 Republican majority, is not at all expected to mount the two-thirds vote needed for conviction, the president's lawyers went so far as to suggest such an outcome would be an "unconstitutional conviction" because of the overly broad articles of impeachment from the House.

The Trump team claims that the constitution requires that senators agree "on the specific basis for conviction" and that there is no way to ensure that the senators agree on which acts are worthy of removal because a single count contains multiple allegations.

Administration officials have argued that similar imprecision applied to the perjury case in the impeachment trial of President Bill Clinton, who was acquitted by the Senate.

Trump's lawyers accused Democrats of diluting the standards for impeachment, an argument that echoed the case made Sunday by one of Trump's attorneys, Alan Dershowitz, who contended in talk shows that impeachable offences must be "criminal-like conduct".

That assertion has been rejected by scholars, and Schiff called it an "absurdist position".

The White House also suggests the House inquiry was lacking because it failed to investigate Biden or his son Hunter, who served on the board of a gas company in Ukraine while his father was vice president. There is no evidence of wrongdoing by either Biden.