WASHINGTON, Jan 31 (Reuters) - President Trump’s impeachment trial reaches a climactic vote on Friday, when senators decide whether to call witnesses and prolong the historic proceeding or instead bring them to the swift conclusion that Trump wants.
Senate Democrats have been arguing throughout the two-week trial that lawmakers need to hear from witnesses like John Bolton, Trump's former national security adviser. But they do not appear to have enough support from Republicans who control the chamber.
Republican Senator Lamar Alexander, who had been undecided, declared late on Thursday that further evidence in the case was unnecessary.
Barring an unforeseen change of heart by another Republican senator, that would leave Democrats short of the 51 votes they need and allow Trump's allies to defeat the request for additional evidence and move towards a final vote that is all but certain to acquit the president.
That final vote could take place late on Friday or on Saturday, congressional sources said.
"The truth is staring us in the eyes," said Democratic Representative Adam Schiff, the lead House prosecutor, said on the Senate floor.
"We know why they don't want John Bolton to testify. It's not that we don't really know what's happened here. They just don't want the American people to hear it in all of its ugly, graphic detail."
The Democratic-controlled House of Representatives impeached Trump in December, formally accusing him of abusing his power for pressuring Ukraine to investigate a political rival, Democratic presidential candidate Joe Biden. The House also charged Trump with obstruction of Congress.
Trump is only the third president in U.S. history to be impeached. A vote of two-thirds of the Senate is required to remove him from office and no Republicans have indicated they will vote to convict.