However, that doesn’t mean GOP senators are not under pressure. In particular, they are facing a choice on the issue of whether witnesses should be called during the trial. Democrats need four Republicans to vote in favor of subpoenas for witnesses or new evidence in order to extend the trial and gather new information. Getting that many will be difficult.
Realistically, there are only perhaps four who would vote in favor of calling witnesses who could testify against the President. That short list includes relative moderates Sens. Susan Collins of Maine and Lisa Murkowski of Alaska, Trump-frustrated conservatives like Sen. Mitt Romney of Utah and endangered senators up for reelection like Sen. Cory Gardner of Colorado.
But there are Democrats who could, feasibly, break with their party — giving Republicans a bigger cushion to work with. And even if Democrats can get four GOP votes to approve witnesses broadly, there will be a separate fight over which specific witnesses get called and it could be that they never get enough votes to compel anyone to testify in the end.
Plus, Trump is likely to try to exert executive privilege over witnesses, prompting some Republicans to suggest they don’t even want to bother trying. It’s a pragmatic approach, maybe, but one which doesn’t do much for the constitutional idea of separation of powers.
Here’s a larger list of senators to watch and why they’re facing pressure to break with their party.
A conservative who has criticized Trump
Conservatives once viewed Trump skeptically. Now the GOP is united behind him. That doesn’t mean there isn’t frustration with his behavior.
Sen. Mitt Romney of Utah (R)
Next reelection: 2024
2016 presidential winner: Trump
2020 rating: Solid Republican
Why he’s important: Romney is a conservative Republican but he’s no friend of Trump and has flashed his independence at times. Romney tried to sabotage Trump’s campaign in 2016 and then Trump embarrassed him by pretending to consider Romney as his secretary of state. But Romney has also complained about how Democrats went about impeachment.
Quote: “I’ve already indicated that I’m interested to hear from John Bolton, perhaps among others,” he said.
Will he flip? He’s keeping everyone guessing
Fighting for reelection
Senators in tough reelection fights are either appealing to the middle in their state, or to the base.
Sen. Susan Collins of Maine (R)

Next reelection: 2020
2016 presidential winner: Hillary Clinton, but Trump got 1 electoral vote under Maine’s split system
2020 rating: Leans Democratic
Why she’s important: Collins is the only Republican to side with Democrats, albeit in a single vote on a minor point, on a portion of rules for the trial. If there’s one Republican likely to vote for witnesses, it’s Collins. She’s in a tough reelection battle in a state that supported Trump. She likes to portray herself as a moderate. She has broken with Trump at key moments (Obamacare) and helped him in others (voting to confirm Supreme Court Justice Brett Kavanaugh).
Will she flip? It’s a good bet she’ll vote with Democrats on something. But probably not on everything.
Sen. Cory Gardner of Colorado (R)

Next reelection: 2020
2016 presidential winner: Clinton
2020 rating: Leans Democratic
Why he’s important: Perhaps the most endangered Republican senator, Gardner will have trouble keeping his seat against former Gov. John Hickenlooper, his likely Democratic rival. His desk, which is usually situation towards the back of the chamber, is situated prominently in the front row on the Republican side of the aisle during the impeachment trial and he’s listened intently and taken lots of notes.
Will he flip? Doubtful. Gardner has not played to moderates like Collins. He’s trying to win in Coloroado with a focus on the GOP base.
Sen. Martha McSally of Arizona (R)

Next reelection: 2020
2016 presidential winner: Trump
2020 rating: Leans Republican
Why she’s important: McSally lost a race for Senate in 2018 to Sen. Kyrsten Sinema, but she was appointed to fill out the term of Sen. John McCain. Now she’s running for election to that seat in 2020. She faces a tough fight against former astronaut Mark Kelly. The fact that she bragged to her supporters about calling CNN’s Manu Raju a hack suggests she’s focused on the Trump base in her state.
Will she flip? Clearly not
Sen. Thom Tillis of North Carolina (R)

Next reelection: 2020
2016 presidential winner: Trump
2020 rating: Tossup
Why he’s important: Barack Obama won North Carolina in 2008 and Democrats have been trying to reclaim it ever since with no luck. It’s a key state again in 2020.
Quote: “It’s time to get back to work on issues that are important to North Carolinians,” he said.
Will he flip? Nope.
Sen. Joni Ernst of Iowa (R)

Next reelection: 2020
2016 presidential winner: Trump
2020 rating: Leans Republican
Why she’s important: Ernst is a stretch. Iowa is less and less a swing state and she’s pretty reliably in Trump’s corner on political issues. Her statements have been very dismissive of impeachment and the need for more information.
Will she flip? Doesn’t seem likely.
Sen. Doug Jones of Alabama (D)

Next reelection: 2020
2016 presidential winner: Trump
2020 rating: Solid Republican
Why he’s important: Jones was lucky to win a special election in 2017 to take the Senate seat left vacant when Jeff Sessions left to become Trump’s first attorney general. Now Jones could face Sessions, who is running for his old seat, in 2020. If there’s a pickup opportunity for Republicans, this is it. While Jones has broken with Democrats on some key issues, he’s all in on impeachment.
Quote: “A real trial has witnesses, a real trial has documents, a real trial has cross-examination, but because of Senator McConnell’s rules, we’re not really in a real trial.”
Will he flip? Nope. He’s committed to witnesses.
Moderates not up for reelection
There are still some fans of bipartisanship in Washington. But impeachment is a very partisan affair.
Sen. Lisa Murkowski of Alaska (R)

Next reelection: 2022
2016 presidential winner: Trump
2020 rating: Solid Republican
Quote: “The House made a decision that they didn’t want to slow things down by having to go through the courts,” Murkowski told CNN. “And yet now they’re basically saying you guys gotta go through the courts. We didn’t, but we need you to.”
Will she flip? We shall see. Her frustrations with the impeachment process are already clear.
Sen. Kyrsten Sinema of Arizona (D)

Next reelection: 2024
2016 presidential winner: Trump
2020 rating: Leans Republican
Why she’s important: Sinema won as a Democrat in Arizona, a state Democrats have been trying to claim. She did it by evolving from an anti-war protester to a full-fledged moderate. But she’s already on the record wanting witnesses at the trial.
Quote: She’s been very quiet.
Will she flip? Not on this.
Sen. Rob Portman of Ohio

Next reelection: 2022
2016 presidential winner: Trump
2020 rating: Leans Republican
Why he’s important: Portman is a fan of bipartisanship and he’s projected that he has an open mind. But he rarely votes with Democrats.
Will he flip? He’s been careful to respect the process.
Sen. Joe Manchin of West Virginia (D)

Next reelection: 2024
2016 presidential winner: Trump
2020 rating: Solid Republican
Why he’s important: Manchin is a political survivor, a Democrat in what’s become a very red state.
Will he flip? He’s staying with his party.
The retiring old guard
Longtime lawmakers who aren’t facing voters again. Will they surprise Washington on their way out the door?
Sen. Lamar Alexander of Tennessee (R)

2016 presidential winner: Trump
2020 rating: Leans Republican
Why he’s important: An institutionalist and a big fan of bipartisanship, Alexander may not like Trump’s behavior, but while he’s often been a voice of reason, he rarely breaks with the party on actual votes. He’s also a close ally of Majority Leader Mitch McConnell who will be relying on him not to buck the party.
Sen. Mike Enzi of Wyoming (R)

2016 presidential winner: Trump
2020 rating: Solid Republican
Why he’s important: He’s a retiring Republican, so who knows what he’ll do.
Quote: He’s stayed very quiet.
Will he flip? Enzi isn’t on anyone’s short list to buck the party.
Sen. Pat Roberts of Kansas (R)

2016 presidential winner: Trump
2020 rating: Solid Republican
Why he’s important: Another retiring Republican, he is not facing voters again.
Will he flip? Roberts isn’t on anyone’s short list to buck the party.
Rust belt senators
Any senator in the Rust Belt, which Trump won, narrowly, in 2016, has to be cognizant of the political battles in their states.
Sen. Pat Toomey of Pennsylvania (R)

Next election: 2022
2016 presidential winner: Trump
2020 rating: Leans Democratic
Why he’s important: It’s more that Pennsylvania is important and Toomey hasn’t closed the door to witnesses.
Quote: “We will allow House managers to make their case, the President’s lawyers to make their defense, and senators to pose questions. At the conclusion of these presentations, the Senate can then decide what, if any, further steps are necessary.”
Will he flip? He hasn’t said no to witnesses. But he’s also been dismissive of impeachment.
Sen. Gary Peters of Michigan (D)

Next election: 2020
2016 presidential winner: Trump
2020 rating: Leans Democratic
Why he’s important: He’s up for reelection in a key state.
Will he flip? Nope.