On Friday, as House managers began making their formal arguments urging the Senate to call new witnesses in President Donald Trump’s impeachment trial, Sen. Lisa Murkowski confirmed that the debate couldn’t make a difference. In a statement, she declared that she was voting with Senate Majority Leader Mitch McConnell to close the trial with no witnesses or document production, giving Republicans the 51 votes they needed to shut it down.

The night before, Sen. Lamar Alexander had issued a statement nudging the door shut on witnesses and documents, arguing that they were unnecessary because Trump had already been proved guilty, and that he would nonetheless refuse to remove him. Murkowski managed to outdo even that breathtaking display of cynicism.

Murkowski explained that she would join her party in rejecting new evidence because the impeachment process was too unfair and too divided along party lines.

“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,” she wrote. “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.”

This is the trick that Republicans in both chambers of Congress—with the exceptions of Rep. Justin Amash, who switched parties after offering his support for impeachment, and perhaps Sens. Mitt Romney and Susan Collins, who still appeared poised to vote for witnesses—played throughout the impeachment proceedings: We can’t vote for impeachment because it’s partisan, and it’s partisan because we’re not voting for impeachment.

Partisanship is whatever partisans say it is. The same procedures that Republicans now deem unfair have been used in past presidential investigations, such as the Benghazi probe, with Republicans behind them. The Trump administration complained about the House interrogating executive branch witnesses without their department counsel present—a rule created and implemented by Republicans when they were in charge of the House and its intelligence committee.

What carried Murkowski beyond the standard Republican impeachment cynicism, though, was her willingness to acknowledge the purely political motives behind her vote. If Murkowski were to have supported calling witnesses, it would have produced a 50-50 Senate tie, forcing Chief Justice John Roberts to decide whether to break it or not. The self-styled umpire of American justice would have had to choose whether to personally side with the president, joining a one-party vote against what opinion polls say are the preferences of large numbers of the American people, or to oppose him. Murkowski said she would vote against witnesses in part because she didn’t want Roberts placed in this bind.

“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,” Murkowski said. “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.”

Rather than a standoff between two branches of government, then, to be resolved by the third, the impeachment trial was a standoff between the two parties. There was nothing Roberts could do to bring it in line with constitutional order, and so Murkowski would not make him try.

“We are sadly at a low point of division in this country,” Murkowski concluded.

That was one point on which her Democratic colleagues were likely to agree.