US Democrats have been dealt a major blow in their efforts to call witnesses at President Trump's impeachment trial.
They needed four Republicans to vote with them to allow witness testimony, but one of the few wavering senators said he would not support the measure.
But giving a setback to Democrat move to impeach Trump, the Republican senator Lamar Alexander refused to vote to democrats. He said there was no need for more evidence to prove Mr Trump had not committed an impeachable offence.
Democrats expected that four Republican senators – Mr Lamar Alexander as well as Mitt Romney, Lisa Murkowski and Susan Collins - would enable them to reach the 51 votes necessary to call witnesses. On Thursday, Ms Collins joined Mr Romney by saying she would also vote for more witnesses.
Mr Alexander's announcement is a sign that Republicans will be able to block the move and put an end to Mr Trump trial with his expected acquittal. A two-thirds majority in the Senate is required to remove him from office, and Republicans hold a 53-47 majority.
The announcement of Mr. Lamar Alexander of not voting in support of impeachment paves the way for the possible acquittal of the president by the Senate as early as Friday. In a statement late on Thursday after a long question-and-answer session at the Senate, Mr Alexander from Tennessee said the Democrats had proven that Mr Trump's actions were "inappropriate".
The Democrats had especially wanted to call the former National Security Adviser, John Bolton, who reportedly said Mr Trump told him directly that he was withholding US military aid to Ukraine until it agreed to investigate his rival, Joe Biden.
If the vote were to end in a tie, it would mean that the motion had failed unless US Supreme Court Chief Justice John Roberts, who is presiding over the trial, decided to break it, which is unlikely.
A bombshell report in the New York Times earlier this week said that Mr Bolton had written in his upcoming book that the president told him directly that military aid was being withheld from Ukraine in exchange for dirt on a Democratic political rival - the key impeachment charge against the president. The report reinvigorated Democrats' attempts to call new witnesses to the trial, and simultaneously energised Republican efforts to push the process through without anyone being called.