Should they agree to call witnesses — and risk hearing the whole case for President Trump unravel before them? Or should they block witnesses — and risk looking as though they didn’t hold a fair trial?

That’s the difficult decision before a handful of Republican senators now, as they prepare for a vote Friday on whether to allow both sides to subpoena witnesses in Trump’s impeachment trial. Democrats’ witness list would almost certainly include former Trump national security adviser John Bolton, who writes in a book that Trump withheld military aid to make his political opponents look bad with the help of a foreign country.

There is no easy way out for Republicans now that we know Bolton says Trump directly linked aid to investigations in Ukraine. Here are some scenarios for how this could end, based on options senators are proposing. They are in order from what we think is least likely to most likely.

4. Democrats get to call whomever they want (read: Bolton) without Republicans calling any of their own witnesses (read: someone to make Trump look good and maybe former vice president Joe Biden look bad).

It’s remarkable that we’ve gotten this far into the trial and a Republican-controlled Senate is unsure whether it can block damaging witnesses for its Republican president. Whatever you think about what would make a fair trial, it’s a big ask to request that Republicans keep digging into their party leader’s actions.

All that’s to say that if Republicans are forced to allow Democrats to call Bolton, they would almost certainly extract some kind of political revenge. Could that mean Trump’s defense team calls members of the Biden family to the stand? Maybe, although that’s risky, for reasons we’ll get into.

Or maybe they have a member of the Trump administration who looks upon Trump’s actions on the military aid more favorably for the president. (Although it’s unclear who that might be, given that a dozen current and former national security officials testified that they thought Trump withheld aid to Ukraine for his own political reasons, and that John Kelly, Trump’s former chief of staff, said he believes Bolton’s version of events.)

3. There is a witness deal, such as a Bolton-for-Biden swap.

The notion of a witness deal never made much sense to begin with. Even though some Senate Democrats were whispering about such a deal to entice Republicans to the table, party leaders couldn’t stand the idea of bringing Biden, a leading 2020 presidential contender, into the Senate to testify about his diplomacy with Ukraine when there is no evidence that he did anything corrupt or unethical.

Plus, some Senate Republicans are understandably skittish about having Biden or his son Hunter Biden (who served on a Ukrainian energy firm’s board at the time his dad was vice president) testify. It might muddy the waters on who’s being investigated, but it also might make senators look extremely political and vindictive, as though they were abusing the very serious power of the Senate chamber to make Trump’s political opponent look bad. Which is the same thing that prompted the House to impeach Trump.

Also, common sense would make clear that Republicans don’t need to make a deal to call witnesses. They control 53 votes and thus could easily pass a majority vote to call one or both of the Bidens to the stand.

But this witness swap is still an option, in part because one moderate Democratic senator, Sen. Joe Manchin III (W.Va.), seems to be entertaining it.

2. There is a stalemate on calling witnesses.

So if neither side wants to budge, what happens if four Republican senators join all Democrats and vote Friday to call witnesses — and then the senators can’t agree on which witnesses they want to hear from? (Under the trial rules the senators set up, witnesses first give interviews under oath in private, and then the Senate votes on whom to hear from.) This scenario is a debate about witnesses within a debate about witnesses; it’s like when lawmakers agree about the broad outlines of legislation and then get stuck forever on the details. Some of that legislation — such as immigration reform — has languished for years. Could a deal on witnesses suffer the same fate?

“All I can say, is I don’t need any more evidence, but if we do call witnesses, we’re not just gonna call one witness. We’re gonna call a bunch of witnesses,” Sen. Lindsey O. Graham (R-S.C.) told reporters Tuesday, words that potentially would make a deal difficult for both sides to reach on who to call.

1. No witnesses testify.

As opening arguments wrapped up Tuesday, my congressional colleagues reported that Senate Majority Leader Mitch McConnell (R-Ky.) told Republican senators that he doesn’t yet have enough votes to block witnesses. That same day, a key voter, Sen. Susan Collins (R-Maine), said it’s “very likely” she’ll join Democrats to hear from witnesses. But that doesn’t mean all is lost for McConnell, who would rather see the trial end this week than continue it with witnesses. He has a few things going for him, including:

  • To date, he has done a remarkable job of keeping his caucus unified, including on a contentious debate about rules at the start of the trial.
  • His partner in all this, Trump, has proved extremely successful at keeping Republican lawmakers loyal to him: Not a single House Republican voted for either count of his impeachment.
  • This first part of the trial has already gone on for two weeks, and bored/tired/restless senators may not want to extend it further.
  • Also, Trump allies such as Graham are vigorously pressing the case that more witnesses means more uncertainty for Trump, and it does not seem as though Republicans want to open that can of worms. Even senators in moderate states, such as Cory Gardner (Colo.), have calculated that to get reelected in November, they need Trump loyalists. Voting to allow a damaging witness to testify against the president could also be a vote to damage their reelection hopes.