Now that former national security adviser John Bolton has said he is willing to testify before the Senate if subpoenaed, Sen. Mitt Romney, a Republican from Utah, wants to hear from him during the impeachment trial.

“I would like to be able to hear from John Bolton. What the process is to make that happen, I don’t have an answer for you,” Romney told reporters on Monday.

Romney is the first GOP senator to speak up since Bolton vowed to help the Senate reach a “final judicial resolution of the still unanswered constitutional questions” regarding President Trump’s interactions with Ukrainian President Volodymyr Zelenskiy. And it shows what could be the first cracks in Senate Majority Leader Mitch McConnell’s resolve not to allow the Democrats to call witnesses, including Bolton, during the impeachment trial.

Senate Democrats need four Republican votes to change the trial rules and allow witnesses. Romney could be one vote. Sens. Susan Collins from Maine and Lisa Murkowski from Alaska could be two more, though both have been hesitant to weigh in on the witness debate so far. Collins, who is up for reelection this year, is far more dependent on the Senate GOP for her upcoming campaign than is Romney, who does not face reelection until 2024.

Murkowski said Monday that she would prefer to delay the debate until after the start of the impeachment trial. "I think we need to do what they did the last time they did this ... and that was to go through a first phase, and then they reassessed after that," she said as she left McConnell’s office. When asked if she would like to hear from Bolton as well, Murkowski said: “I think what we need to do is get to the first step, which is having articles to deal with.”

Collins has said much the same, calling Sen. Chuck Schumer’s behavior a “typical, inappropriate approach that indicates he’s not really sincerely interested in negotiation.” A sign of good faith would be to pass the articles of impeachment onto the Senate, begin the trial, and then conduct the debate over witnesses, she said. “The process moved to a period during which the Senate debated and voted that three witnesses should be deposed. I believe that this process — the Clinton approach — worked well,” she said.

It’s unlikely that Collins will break with McConnell, but there’s a chance Murkowski might. Murkowski was one of the only Senate Republicans to vote against Supreme Court Justice Brett Kavanaugh’s confirmation, whereas Collins voted to support it. And Murkowski has been openly critical of McConnell throughout this process and has made it clear she doesn’t want the Senate GOP to cozy up to the White House.

Collins seems to have a much bigger target on her back from Democrats. Just this week, the Democratic Senatorial Campaign Committee launched a new website that takes aim at Collins’s remarks on impeachment in light of her past comments during former President Bill Clinton’s trial. Collins needs the Senate GOP’s support just as much as they need her vote, so it’s unlikely she’ll bail on them now.

McConnell might lose Romney and Murkowski, but that won’t matter if he can hold onto Collins’s support. Even if he did lose Collins, Senate Democrats would still need one more Republican vote to win the witness fight. And when faced with a choice between Schumer or McConnell, few Republicans, moderate or not, would need to think before answering.