U.S. Sen. Susan Collins has built her political career on taking moderate, well-reasoned approaches to most issues and by responding to various controversies with level-headed diplomacy.

They are among the reasons the Republican has been elected four times, including with 68 percent support in 2014, and why she routinely is ranked among the most popular elected officials in the country.

Donald Trump, though, is testing the senator’s measured style.

On Monday, Collins – along with many other top Republicans – denounced Trump’s criticism of a judge’s ethnic background as “absolutely unacceptable,” and said it does “not represent American values,” but she stopped short of saying whether she will endorse or vote for him come November.

Collins’ balancing act on Trump is not unique. Republican leaders across the country, from U.S. House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell to former Trump rivals Ted Cruz and Marco Rubio, are being asked with increasing regularity to respond to various unfiltered statements made by the presumptive presidential nominee. Ryan on Tuesday called Trump’s latest comment, in which he implied that Judge Gonzalo Curiel’s Mexican heritage meant he could not be impartial toward Trump, the “textbook definition” of racism. Trump, meanwhile, put out a statement late Tuesday saying his comments were “misconstrued.”

Collins said Tuesday that being asked to support or condemn Trump’s statements is not what she wants to be doing.

“I like public policy and would much prefer to be discussing the appropriations bill that I managed on the floor or the work we’re doing in the health committee to create innovative medical research … or any number of other things,” Collins said in an interview Tuesday. “Like so many Americans, I am struggling to figure out the presidential race. This has been the most unpredictable race that I’ve seen since I’ve been eligible to vote.”

As a politician, Collins might be the exact opposite of Trump. She rarely criticizes opponents, and when she does, it’s not personal. She never makes off-the-cuff remarks, the signature of Trump’s campaign.

“I don’t think she ever speaks without carefully considering what she’s going to say,” said Mark Brewer, a political science professor at the University of Maine. “But she’s also vastly different in terms of substance. And I think she’d much prefer to talk substance. This has to be driving her crazy.”

Collins, unlike some of her Senate colleagues, does not have to worry about re-election this year, which could be a factor in how she reacts or responds publicly to Trump.

By comparison, Sen. Kelly Ayotte of New Hampshire is in a tight race against her Democratic challenger, Gov. Maggie Hassan, and Ayotte has faced pressure to denounce Trump or risk losing support in her own race.

After joining other Republicans on Monday in calling out Trump’s comment about Judge Curiel, Ayotte tap-danced around the question of whether she would support him by saying she would vote for Trump but not endorse him.

“For Collins and other respected Republicans, they probably see a much bigger risk of being seen as too embracing of Trump or too slow to stand up to him than in calling him out,” Brewer said.

Ross Baker, a professor of political science at Rutgers University and former senior adviser to several senators, said he’s not surprised to see Collins criticize Trump.

“I think within the Senate Republicans, they don’t mind this as much from her as they might if it were someone else,” he said. “They sort of expect it from her. She occupies her own niche in the party. But at the same time, she didn’t need to say anything on this.”

Baker actually thinks Trump has bigger problems with very conservative Republicans who don’t believe the candidate shares their values but who are unwilling to say so publicly.

During Trump’s improbable rise from a candidate who wasn’t taken seriously to the brink of becoming the Republican nominee, Collins, who previously endorsed and campaigned for Jeb Bush, has yet to fully embrace Trump and has spoken critically about him on occasion. In December, after Trump said he would consider banning Muslims from entering the country, Collins said the idea “does not reflect our American values.” In May, she warned Trump to knock off the personal insults, particularly against women.

On Tuesday, Collins said she’ll continue to call out Trump if necessary, but she’s also holding out hope that he changes his ways.

She said she has criticized presumptive Democratic presidential nominee Hillary Clinton, too, although that hasn’t gotten as much attention.

“I have told reporters that I was troubled that Hillary Clinton and her top aides did not cooperate with the investigation done by the State Department’s inspector general into use of a private server for emails,” Collins said. “Her refusal to cooperate with a legitimate investigation is troubling.”

Brewer said unless Trump changes, Collins and others will continue to be asked about him.

“I’m sure that Collins and other Republicans are hoping he changes his stripes,” he said. “It would make it easier for them if they can say, ‘He’s learned his lesson.’ ”

Baker said senators like Collins are likely to face significant pressure to “stand fast in the ranks.” Sen. Ben Sasse, a Republican from Nebraska, has been criticized widely by members of his party for failing to back Trump and for encouraging others to do the same.

Collins, who is friendly with Clinton from their time in the Senate together, has said she likely would not vote for the Democrat but hasn’t ruled it out entirely. She also hasn’t ruled out supporting a third-party candidate, should one emerge. In the past, she has always supported her party’s nominee.

One thing she probably won’t do in November is stay home.

“It would be very difficult for me to not vote, but it’s a long ways between now and Election Day,” she said. “There is plenty of time for me to continue to evaluate the candidates.”