Washington, Jan 22 (AFP) In a somber and hushed Senate chamber, Democrats began presenting their opening arguments in the impeachment trial of President Donald Trump on Wednesday, accusing him of using the power of his office to cheat in the upcoming election.

Adam Schiff, the head of the prosecution team from the House of Representatives, took the floor of the Senate after lawmakers were told by the sergeant-at-arms to remain silent during the historic proceedings.

"President Trump solicited foreign interference in our democratic elections, abusing the powers of his office to seek help from abroad to improve his re-election prospects at home," the California lawmaker said.

"And when he was caught, he used the powers of that office to obstruct the investigation into his own misconduct," said Schiff, who headed the probe that led to Trump's December 18 impeachment by the Democratic-controlled House.

Schiff shrugged off Republican arguments that American voters -- and not the Senate -- should decide in November whether Trump should remain in the White House.

"The president's misconduct cannot be decided at the ballot box for we cannot be assured that the vote will be fairly won," Schiff said. "The president has shown that he believes he is above the law and scornful of restraint."

Trump is accused of withholding military aid from Ukraine to pressure his Ukrainian counterpart to announce an investigation into Democrat Joe Biden, his potential presidential opponent.

Schiff appealed to the 100 senators to put aside partisanship in deciding Trump's fate.

"The Constitution entrusts to you the responsibility of acting as impartial jurors," he said. "Our duty is to the constitution and the rule of law."

Republicans, who enjoy a 53 to 47 edge in the Senate, have shown little inclination, however, to break ranks with the president.

A two-thirds majority -- or 67 senators -- is required to remove a president from office and a series of votes on the ground rules for the trial on Tuesday followed strict party lines.

Republicans shot down a series of bids by Democrats to introduce White House witnesses and documents during nearly 13 hours of acrimonious debate that lasted late into the night.

Trump, who was attending the World Economic Forum in Davos as the historic trial got underway on Tuesday, blasted the proceedings as a "witchhunt" and a "hoax" and said he expected the Republican-led Senate to clear him "fairly quickly."

The president defended the Republicans' rejection of Democratic efforts to force former national security advisor John Bolton and others to testify at his trial saying of Bolton, for example, that it would present a "national security problem."

"John, he knows some of my thoughts," Trump said. "He knows what I think about leaders. What happens if he reveals what I think about a certain leader and it's not very positive?"

Schiff and the other House managers have 24 hours over three days to make their case that Trump is guilty of abuse of power and obstruction of Congress.

White House lawyers will then have 24 hours to present their defence.

On Tuesday, House prosecutors and White House lawyers squared off in fiery exchanges over the rules for just the third impeachment trial in US history, leading Democratic Senator Chuck Schumer to lash out at Republican Senate leader Mitch McConnell.

"If there's one thing we learned here on the Senate floor it's that Leader McConnell and Senate Republicans don't want a fair trial that considers all the evidence," Schumer said.

After both sides present their cases, senators will have an opportunity to ask written questions to be read out aloud by US Supreme Court Chief Justice John Roberts, presiding over the trial.

Roberts' role is mostly ceremonial but he did warn both sides, near the end of a marathon day marked by bitter clashes, to watch their decorum.

"Those addressing the Senate should remember where they are," Roberts said.

Trump's lawyers, led by Pat Cipollone and Jay Sekulow, argued on Tuesday that the House impeachment probe had been unfair to the president.

"They are trying to remove President Trump's name from the ballot and they can't prove their case," Cipollone said.

The next few days are likely to be an endurance test for members of the Senate, some of whom are in their 80s.

Barred from having their phones and computers at their desks, they scribbled on notepads, chatted quietly, fidgeted and stretched on Tuesday.

The four Democratic senators seeking to challenge Trump for the White House have been forced to take time off from campaigning ahead of the first state caucuses to choose their party's nominee in Iowa on February 3.

"We're all there to do our duty," said Minnesota Senator Amy Klobuchar, who is seeking the nomination along with Vermont Senator Bernie Sanders, Massachusetts Senator Elizabeth Warren and Colorado Senator Michael Bennet. (AFP)

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