The historic impeachment trial of Donald Trump opened Thursday in the US Senate, as lawmakers took a solemn oath to be "impartial" in deciding whether to force the 45th US president from office.
In a hushed chamber, Supreme Court Chief Justice John Roberts, clad in a traditional black robe, raised his right hand as he was sworn in to preside over the trial. He then administered the oath to senators in turn, to convene the third court of impeachment in American history.
Roberts asked if they swore to deliver "impartial justice" according to the US Constitution, and 99 lawmakers -- one was absent -- responded in unison: "I do."
Earlier in the day in a deeply symbolic moment, the two articles of impeachment -- charging Trump with abuse of power and obstruction of Congress -- were read out on the Senate floor.
The Senate Sergeant of Arms Michael Stenger issued a warning as proceedings got underway.
"Hear ye, hear ye, hear ye," Stenger said, commanding senators to "keep silent, on pain of imprisonment."
Adam Schiff, the chairman of the House Intelligence Committee who will serve as lead prosecutor for the trial, read the charges accusing Trump of "high crimes and misdemeanors."
Trump has ridiculed the impeachment process for months, and he responded to the opening of the trial by once more branding it a "hoax."
"I think it should go very quickly," Trump told reporters in the Oval Office.
"It's totally partisan," Trump said. "I've got to go through a hoax, a phony hoax put out by the Democrats so they can try and win an election."
The Democratic-controlled House, in an overwhelmingly partisan vote, impeached Trump on December 18 over his dealings with Ukraine and subsequent efforts to obstruct the investigation into the affair.
Impeachment rules require a two-thirds Senate majority to convict and remove a president, and Trump's acquittal is widely expected in the Republican-dominated Senate.
Justice Roberts, 64, was appointed to the nation's top court by president George W. Bush, and will preside over the duration of the trial, which is expected to last two weeks.
After the senators' swearing in, the Senate adjourned until 1:00 pm (1800 GMT) on Tuesday, when the prosecution begins laying out its case against the president.
One senator -- Republican James Inhofe -- was absent due to a family medical emergency but said he would be sworn in "with no delay" on Tuesday, when Trump's impeachment trial begins in earnest.
'Senate's time is at hand'
Trump is accused of abuse of power for withholding military aid to Ukraine and a White House meeting for the country's president in exchange for an investigation into his potential presidential election rival Democrat Joe Biden.
The nonpartisan Government Accountability Office concluded in a report released Thursday that the White House violated federal law by putting a hold on the congressionally-approved funds for Ukraine.
"Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law," according to the GAO, a congressional watchdog.
The second article of impeachment relates to Trump's refusal to provide witnesses and documents to House impeachment investigators in defiance of congressional subpoenas.
Senate Majority Leader Mitch McConnell has been extremely critical of Trump's impeachment by the House and Democrats have accused him of planning to oversee a "sham" trial in the Senate.
McConnell has said he would coordinate the defense of Trump in the Senate with the White House.
"It was a transparently partisan performance from beginning to end," McConnell said of the House impeachment. "But it's not what this process will be going forward.
"The House's hour is over," the Republican senator from Kentucky said. "The Senate's time is at hand."
House Speaker Nancy Pelosi said Trump had given the House no option.
"It is a sad day for America," Pelosi told reporters. "We were given no choice."
Trump's actions undermined national security, were a violation of his oath of office and "jeopardized the integrity of our elections," she said.
For weeks Pelosi held back on delivering the articles to the Senate as she pressured McConnell to agree to subpoena the witnesses and documents that the White House blocked from the probe.
McConnell has refused to commit, saying the issue will only be decided after the trial's opening arguments and questioning.
A Trump administration official told reporters they expect the trial to last no longer than two weeks, suggesting McConnell could use his 53-47 Republican majority to stifle calls for witnesses and quickly take the charges to a vote.
Aside from Schiff the prosecution team will include Judiciary Committee chair Jerry Nadler; House Democratic Caucus chair Hakeem Jeffries; Zoe Lofgren, a veteran of two previous impeachment investigations; and three others.
© Agence France-Presse