Democrats needed four Republican senators to side with them in a vote to call more witnesses in the impeachment trial against President Donald Trump.
US Democrats' efforts to hear more testimony in the impeachment trial against President Donald Trump were all but dashed on Thursday after a Republican Senator opposed calling more witnesses.
The decision by Republican Senator Lamar Alexander means Trump could be acquitted on Friday.
Democrats needed four senators from the Republican party — which holds a majority in the Senate — to vote with them in order to call more witnesses.
Former Republican presidential candidate Mitt Romney and Susan Collins, the Republican Senator of Maine had both already announced they would support hearing more testimony while Lisa Murkowski of Alaska had asked for more time to make her decision.
But Alexander, a moderate Republican, broke the stalemate, releasing a statement in which he affirmed that "there is no need for more evidence".
He said that "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" but that "the Constitution does not give the Senate the power to remove the president from office and ban him from this year’s ballot simply for actions that are inappropriate".
Senators are expected to vote on Friday on whether to call more witnesses. If they lose the vote, the trial could be brought to an abrupt end and result in Trump's acquittal.
Nancy Pelosi, the Democratic Speaker of the House, had said earlier in the day that if Republicans senators rejected the motion, it would amount to a "cover-up".
"You cannot be acquitted if you don't have a trial. You don't have a trial if you don't have witnesses and documentation," she wrote on Twitter.