Susan Collins and Lisa Murkowski get the cover they need to vote for witnesses in Trump's impeachment trial

Analysis

• Republican senators are poised on Friday to block witnesses from testifying in President Donald Trump's impeachment trial.
• A key turning point came on Thursday night when Sen. Lamar Alexander announced he'd vote "no" on the motion to call witnesses.
• Alexander's decision gave cover to two vulnerable GOP senators, Susan Collins of Maine and Lisa Murkowski of Alaska, who have both since said they'll vote "yes" on witnesses.
• Democrats need four Republican votes to reach a 51-vote majority and pass the motion, but just three Republicans appear ready to vote with them on the issue.
• Collins and Murkowski would be able to tell their constituents and supporters back home — including many independents and Democrats — that they showed independence from their party at a key moment.
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Republican senators are poised to block witnesses from testifying in President Donald Trump's impeachment trial in a vote on Friday that would move the trial into its final stage.

A key turning point came on Thursday night when Sen. Lamar Alexander, a Tennessee Republican who was considered a possible vote for witnesses, said that while Trump's actions concerning Ukraine were "inappropriate," he'd vote "no" on the motion.

"Let the people decide," he concluded, referring to the 2020 presidential election.

But three Republican senators appear ready to defect from their party. Notably, that would fall one short of the four GOP votes Democrats need to reach a 51-person majority and pass the motion.

Sens. Susan Collins of Maine and Mitt Romney of Utah announced on Thursday that they'd vote "yes" on the motion to call witnesses. And Sen. Lisa Murkowski of Alaska appears ready to join them.

"I believe hearing from certain witnesses would give each side the opportunity to more fully and fairly make their case, resolve any ambiguities, and provide additional clarity," Collins said in a statement Thursday night.

Also on Thursday night, Murkowski asked Trump's defense team why Americans shouldn't hear more evidence, including from the former national security adviser John Bolton.

"This dispute about material facts weighs in favor of calling additional witnesses with direct knowledge," Murkowski said. "Why should this body not call Ambassador Bolton?"

Democrats have been pushing to hear from four key witnesses, including Bolton and Mick Mulvaney, the acting White House chief of staff, both of whom were direct witnesses to the president's Ukraine pressure campaign that is at the center of his impeachment.

The political ramifications of this key vote for Trump's impeachment trial are unclear. But if Collins and Murkowski both vote to include witnesses, they'd be able to tell their constituents and supporters back home — including many independents and Democrats — that they showed independence from their party at a key moment.

If Republicans succeed in blocking witnesses, the trial will proceed to its final stages. The timing for a vote to remove or acquit the president remains unclear and will depend on whether senators want to debate into the night on Friday or opt to adjourn and continue the process into the weekend.

An Insider poll conducted this week found that many Americans were in favor of hearing from witnesses.

When asked "What best describes your view about the impeachment proceedings?" just 13% of American adults said they didn't see a need for witnesses, while 49% said they wanted some combination of witnesses — just direct witnesses, just indirect witnesses, or both.