USA Today: WASHINGTON – Sen. Lisa Murkowski, R-Alaska, announced Friday she will not vote to call witnesses in President Donald Trump’s impeachment trial, virtually assuring that Democrats won’t have the 51 votes needed to hear from former national security adviser John Bolton or others.

Murkowski also said the trial had not been fair and that Congress had failed as an institution.

“Given the partisan nature of this impeachment from the very beginning and throughout, I have come to the conclusion that there will be no fair trial in the Senate. I don’t believe the continuation of this process will change anything. It is sad for me to admit that, as an institution, the Congress has failed,” she said.

“It has also become clear some of my colleagues intend to further politicize this process, and drag the Supreme Court into the fray, while attacking the chief justice. I will not stand for nor support that effort. We have already degraded this institution for partisan political benefit, and I will not enable those who wish to pull down another.

Murkowski was the last of a handful of Republicans who had expressed a potential openness to witnesses.

That likely sets up a 51-49 split in the closely divided chamber against considering additional evidence. Democrats need four Republicans to side with them to continue the trial.

The Senate will hear up to four hours of debate from President Trump’s lawyers and from the Democratic House impeachment managers, starting just after 1 p.m., on whether to call witnesses. And then there will be a vote on whether to consider witnesses, probably around 5 p.m.

That vote is expected to fail or end in a tie. Chief Justice John Roberts, the presiding officer over the trial, could break the tie with a ruling in favor of considering witnesses, or against it, but he is not expected to do so. And if he does not rule on a tie vote, the motion fails and witnesses will not even be considered.

WATCH LIVE: The Senate impeachment trial of Donald Trump

Two Key Republicans Split Democrats Unlikely To Get Witnesses

After that, the delay tactics available to Democrats are virtually endless. Any motion or amendment is “in order,” meaning Republicans in the majority have no power to force an end to deliberations. If Democrats want to propose motions, which usually provide for up to two hours of debate, they can do so as long as they want.

But senators will still not be able to speak. All the speaking will be done by the president’s lawyers and House impeachment managers.

Impeachment endgame