Donald Trump’s impeachment trial has started with senators being sworn in as jurors and the charges against the president read out.
As senators took their oaths, a congressional watchdog found the White House broke the law by withholding security aid for Ukraine approved by Congress.
It is unclear whether the assessment from the nonpartisan Government Accountability Office will feature in the president’s trial in the Republican-led Senate as it is not known if new evidence will be considered.
As the impeachment trial officially started, seven House representatives who have been appointed as impeachment prosecutors walked across the Capitol for the second day after delivering the charges to the Senate on Wednesday.
“Hear ye, hear ye, hear ye!” called out the Senate’s sergeant-at-arms as he started the ceremonial protocol ahead of the charges being read out.
Lead prosecutor Adam Schiff, who also leads the intelligence committee, then read out the formal charges against the president from the well of the Senate usually reserved for senators.
Chief justice John Roberts, who will preside over the trial, later took an oath to preside over the trial then swore in 99 out of 100 senators who will serve as jurors, as they promised to deliver “impartial justice”.
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One senator, Republican Jim Inhofe, was at home in Oklahoma to be with an ill family member, according to his office, but will sign the oath later.
Thursday’s ceremony was the formal start of the impeachment trial, but the actual arguments will not start until next Tuesday.
Following the senators being sworn in, Mr Trump tweeted: “I JUST GOT IMPEACHED FOR MAKING A PERFECT PHONE CALL!”
Mr Trump is accused of abusing his office by asking the Ukrainian president to investigate the son of his political rival Joe Biden and withholding $391m (£299m) in security aid for Ukraine until he agreed to.
However, the president has dismissed the charges as a “hoax”.
He suggested Republican senators should vote to dismiss the impeachment articles without hearing any arguments, but they have indicated that is not something they will do.
The Senate is expected to acquit Mr Trump, as none of its 53 Republicans voiced support for removing him – a step that requires a two-thirds majority.
There is an ongoing debate over how and when witnesses will be called, with Mr Trump’s administration saying they should not be called, while most in the House say they should.
During Bill Clinton’s impeachment trial no witnesses were called, however they had all given evidence before the trial, and as a House representative said on Wednesday: “Did we really want to discuss sex in the Senate?”
Republicans control the Senate, the US’s second chamber, by 53-47 and it would take 51 votes to approve rules or call witnesses during the trial.
If four Republican senators joined the Democrats’ side, they could insist on new evidence.
Mr Trump’s trial will be only the third in US presidential history, after Andrew Johnson and President Clinton, and it will be the second to be televised.