US House of Representatives Speaker Nancy Pelosi has warned Republicans not to become “the president’s henchmen” as the Trump impeachment trial began.
Mrs Pelosi renewed her call for fresh evidence and witnesses to be admitted in the forthcoming hearings.
Pre-trial proceedings have begun with the charges being formally read aloud to the Senate.
Donald Trump is the third US president ever to be impeached, but the previous two were not removed from office.
He is accused of abuse of power and obstruction of Congress, and brands the case against him as a politically motivated “hoax”.
Speaking at her weekly press conference on Thursday, Mrs Pelosi said: “I hope that the senators do not become part of the president’s henchmen.”
She spoke shortly before the trial of the president got underway in the US Senate, which is controlled by the president’s fellow Republicans.
The articles of impeachment were read out on the floor of the chamber by lead prosecutor Adam Schiff.
The Democratic congressman said no president had ever sought to impede an impeachment investigation so thoroughly.
Mr Schiff is one of seven impeachment managers who will make the case against the president.
Supreme Court Chief Justice John Roberts will be sworn in as presiding judge before the senators take their oaths to do “impartial justice” as jurors.
Mr Trump’s defence team has not been formally announced, but White House lawyers Pat Cipollone and Jay Sekulow have been tipped to lead it.
The House officially handed over the impeachment proceedings on Wednesday, when Mrs Pelosi signed the articles of impeachment and they were walked across the Capitol in a procession and delivered to the Senate.
Republicans have criticised Mrs Pelosi over the signing event, mocking her for handing out commemorative pens decorated with her signature.
Republican Senate leader Mitch McConnell said on Thursday, before trial proceedings began: “Nothing says seriousness and sobriety like handing out souvenirs as though this were a happy bill signing instead of the gravest process in our Constitution.”
Opening statements in the trial are expected next Tuesday.
Read Also: White House ‘Broke Law’ By Withholding Ukraine Aid
This means the trial will likely still be under way in early February when Iowa and New Hampshire hold the first contests to pick the eventual Democratic presidential candidate.
This timing has been a boon to presidential frontrunners Joe Biden and Pete Buttigieg, as rivals Bernie Sanders and Elizabeth Warren will both be off the campaign trail to attend the trial.
Mrs Warren and Mr Sanders’ teams have both scheduled intense campaigning in Iowa during the weekends leading up to the vote on 3 February, Reuters reported.
During the weekdays, when they are compelled to be in Washington, both are considering having supporters or family members host events, or scheduling remote appearances.
BBC NEWS