Democrats sounded resigned to defeat on Friday in their bid to call witnesses at US President Donald Trump's Senate impeachment trial, predicting his fellow Republicans would move swiftly to acquit him and leave him in office.
"Tonight, all signs point to a rushed acquittal of an impeached president," Patty Murray, a member of the Senate Democratic leadership, told reporters.
The Senate was due to resume the proceedings with further arguments from Trump's legal team and the House of Representatives Democrats serving as prosecutors. The Senate was due later on Friday to vote on whether to allow witnesses.
The timing of a final vote on whether to convict Trump was unclear. Republican senators had said it could take place late on Friday or on Saturday. But some senators said the final vote may be put off until next week, perhaps until Wednesday.
A second Republican senator - Mitt Romney - declared support on Friday for calling such witnesses as John Bolton, Trump's former national security adviser. But Democrats were still short of gaining the four Republican votes needed to prolong the trial with testimony that Trump's allies have fought to prevent.
Romney, the 2012 Republican presidential nominee and sometime critic of Trump, joined fellow moderate Susan Collins as the only ones among the 53 Republican senators in the 100-seat chamber to support voting for witnesses.
Barring an unforeseen change of heart by other Republican senators before a final vote on the articles, Trump's allies seemed assured of defeating the request for testimony.
"If my Republican colleagues refuse to even consider witnesses and documents in this trial, this country is headed towards the greatest cover-up since Watergate," Chuck Schumer, the top Senate Democrat, told reporters, referring to the corruption scandal that prompted Richard Nixon in 1974 to become the only US president to resign.
Acquittal in a "sham trial" would prompt Trump to conclude he "can try to cheat in his election again, something that eats at the roots of our democracy," Schumer said. Trump is seeking re-election in a Nov. 3 vote.
Republican Senator Lamar Alexander, who had been undecided, said late on Thursday that Democrats had proven the case against Trump but that the president's actions did "not meet the United States Constitution's high bar for an impeachable offense."
Alexander said it was "inappropriate for the president to ask a foreign leader to investigate his political opponent and to withhold United States aid to encourage that investigation."
The Democratic-led House voted to impeach Trump on Dec. 18. It charged him with abuse of power for asking Ukraine to investigate a political rival, Democratic presidential candidate Joe Biden. It also charged him with obstruction of Congress for blocking current and former officials from providing testimony or documents to the House.
A two-thirds majority in the Senate is required to remove Trump from office. No Republicans have yet indicated they will vote to convict. Trump is only the third president in US history to be impeached.
NEW BOLTON ACCUSATIONS
The New York Times, which previously reported on allegations made in Bolton's unpublished book manuscript that go to the heart of impeachment charges, on Friday reported on additional material in the book.
The Times previously reported that Bolton - contradicting Trump's version of events - wrote that the president told him he wanted to freeze $391 million in security aid to Ukraine until Kiev pursued investigations of Democrats, including Biden and the former vice president's son, Hunter Biden.
On Friday, the Times reported that Bolton also wrote that Trump directed him in May to assist in a pressure campaign to get damaging information on Democrats from Ukrainian officials.
Bolton wrote that Trump issued the order in a White House conversation that also included acting White House Chief of Staff Mick Mulvaney, personal lawyer Rudy Giuliani and White House Counsel Pat Cipollone, who is part of the president's impeachment defense team, the Times reported.
Bolton wrote that Trump told him to call Ukrainian President Volodymyr Zelenskiy to ensure Zelenskiy would meet with Giuliani, a key player in the pressure campaign, the Times reported.
The White House has objected to the publication of the book, saying it contains classified information that could harm national security if disclosed.
Democrats have said Trump abused his power by using the security aid - passed by Congress to help Ukraine battle Russia-backed separatists - and a coveted White House invitation to Zelenskiy as leverage to get a foreign power to smear a political rival.
Senate Democrats have been arguing throughout the two weeks of proceedings that lawmakers need to hear from witnesses to ensure a fair trial.
Trump's Republican allies have sought to keep the trial on a fast track and minimize any damage to the president. Trump denies any wrongdoing.
Trump's acquittal would allow him to claim vindication just as Democrats hold the first of the state-by-state nominating contests on Monday in Iowa to choose the party's nominee to challenge Trump in the election. Biden is a leading contender to face Trump in the November election.