A moment of uncertainty has entered the Trump impeachment proceedings.

There is now a witness. It is Trump's former national security adviser, John Bolton. He has a book coming out in March, outlines of which were leaked to The New York Times.

"President Trump told his national security adviser in August that he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats including the Bidens," said the NYT report.

You could call it extortion, a demand for a bribe, or a quid pro quo. In this context, Bolton is an extraordinarily credible witness. Previously, he was a neo-con hero to I-want-more-war Republicans, and a dangerous right-wing loon to Democrats. It is relatively hard for Republicans to attack him, though they have already started and will continue to do so.

Bolton's claim directly undercuts Trump's defence. At least as to what actually happened.

His book also depicts acting Chief of Staff Mick Mulvaney, Secretary of State Mike Pompeo, and Attorney General William Barr as all telling lies about what they knew and when they knew it.

Until this moment it seemed absolutely certain that the Senate Republicans would not vote to find Trump guilty and would not vote to remove him from office, that they would not even allow additional witnesses and documents and would do all they could to get it over with as quickly as possible.

That was settled a long time ago.

In November, a group of Republican senators, including Lindsey Graham, Mike Lee, Ron Johnson, Ted Cruz, Tom Cotton, and John Kennedy (of Louisiana, no relation to the Massachusetts Kennedys) went to the White House to meet with Pat Cipollone, Trump's White House lawyer, Mick Mulvaney, Jared Kushner, Kellyanne Conway and others. What they discussed was how soon the trial part of impeachment in the Senate could be dismissed.

Back in mid-December, before it even came to the Senate, Lindsey Graham said "I have made up my mind. I'm not trying to pretend to be a fair juror here. ... [it's] just a partisan nonsense. ... this thing will come to the Senate and it will die quickly and I will do everything I can to make it die quickly."

Mitch McConnell announced publicly that the fix is in. "I'm coordinating with White House counsel. There will be no difference between the president's position and our position." No embarrassment, no shame, about it.

The facts were not supposed to matter.

Their defence does not seek to refute the prosecution's facts. It seeks to dismiss the prosecution as illegitimate, to complain that the Democrats held "secret" hearings even though Republicans were there, and to maintain that they did not permit the president to cross-examine those witnesses, even though his Republican defenders could do so on his behalf.

It seeks to assert that the blanket refusal of the White House to supply documents and its order to all members of the executive branch not to testify were a carefully considered legal examination applied issue by issue.

In their universe, the desire of the Democrats to get Trump completely erases the significance of whether there are acts for which Trump should be gotten, while Republican righteousness in defending Trump is so great that right or wrong, it is always right.

The idea that there are actual "moderate Republicans" like Dwight Eisenhower, Nelson Rockefeller, George H W Bush, or even John McCain is a fantasy. To claim that Trump has changed the Republican Party is an excuse. All that he has done is allow them to come out of the closet as nakedly concerned about keeping power and cutting taxes for the rich and not have to bother with dressing up as thoughtful, sensible servants of the public.

Pundits, commentators and editorial writers in search of drama have been pushing the story that there are four - or possibly more - Republicans who could switch and vote in favour of subpoenas for witnesses and documents. Four names were usually floated: Susan Collins, Lisa Murkowski, Lamar Alexander, and Mitt Romney.

Until Bolton, that had to be considered a sad, even pathetic fantasy.

Now, Collins and Romney have stepped up. Collins said the reports "strengthen the case for witnesses". Romney said, "I think it's increasingly likely that other Republicans will join those of us who think we should hear from John Bolton."

The knowledge that there is an extremely credible first-hand witness waiting and willing to testify just outside the room should change things. Now that the whole world (of those who pay attention) knows that he will say that Trump engaged in an extortion scheme (though he might not use that word), we will also know that senators who refuse to let him testify will be engaging in an actual cover-up.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.