Democrats appeared to have fallen short Thursday in their bid to secure the votes needed to call witnesses in President Trump's impeachment trial, clearing the way for Trump's likely acquittal as early as this weekend.

Democrats had urged a handful of Republicans to support their effort to call witnesses, but their hopes appeared dashed when Republican Sen. 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 had concluded.