WASHINGTON                -              Democrats have worked to get at least four Republicans to support the effort, but their hopes appeared dashed when Republican Senator Lamar Alexander, who had been undecided, declared further evidence in the case was unnecessary.

“There is no need for more evidence to prove something that has already been proven and that does not meet the United States constitution’s high bar for an impeachable offense,” Alexander said in a statement after the evening session. Barring an unforeseen change of heart by another Republican senator, it appeared Alexander’s decision would bring a swifter conclusion to Trump’s two-week trial.

Republican Senator Susan Collins broke with her party and announced her support for witnesses. But Democrats needed at least of three of her colleagues to defect and give them the 51 votes needed to call witnesses and prolong the trial. Late on Thursday, Republican Senator Lisa Murkowski said, “I am going to go reflect on what I have heard, reread my notes and decide whether I need to hear more.” A 50-50 tie on the question of witness testimony and additional evidence could result if Murkowski and Senator Mitt Romney join Collins in backing the additional evidence.

Such a deadlock would mean that the drive for witnesses would fail, unless U.S. Supreme Court Chief Justice John Roberts, who is presiding over the Senate trial, voted to break the tie. The backing of two-thirds of the Senate is required to remove Trump. He is unlikely to be convicted.

Democrats had hoped to hear from former National Security Adviser John Bolton after a report - which he has not denied - that he planned to say in an upcoming book that Trump told him he wanted to freeze $391 million in U.S. military aid for Ukraine until it investigated Democratic presidential contender Joe Biden and his son Hunter, who worked for a Ukrainian energy firm while his father was vice president.

The Democratic-controlled House of Representatives impeached Trump in December, formally accusing him of abusing his power for pressuring Ukraine to investigate the Bidens. The House also charged Trump with obstruction of Congress. Trump’s acquittal would allow him to claim vindication just as the Democratic Party holds its first nominating contest for the Nov. 3 election in Iowa on Monday.

Trump held a rally in Des Moines, Iowa, on Thursday and slammed the trial, calling it an effort by Democrats to overthrow his 2016 election victory.