Washington • Sen. Mitt Romney’s approval among Republicans and independents appears to be slipping as he heads into the impeachment trial of President Donald Trump, where the Utah Republican is breaking with the president and GOP leaders by calling for at least one witness, former National Security Adviser John Bolton, to testify.

Romney, though, appears to be gaining traction with Democrats who are giving him better marks.

A Morning Consult poll shows an 18 percent drop of Romney’s approval rating among Republicans in the last four months of 2019 as compared to the quarter before that. And 9% of independents swung to disapproving of Romney quarter over quarter, the poll found.

A majority of Utah Republicans still back Romney — 57% in the last four months of 2019 — but that’s down from 65% the prior quarter.

Romney, a freshman, got a bump with Democrats late last year, with 46% of them approving of him in the fourth quarter compared to 42% the months before.

Overall, 48% of Utah voters support Romney’s job performance compared to 38% who disapprove. Some 14% weren’t sure.

Romney's office did not respond to a request for comment.

Romney is still more popular than his colleague Sen. Mike Lee, who earns approval from 46% of Utah voters compared to disapproval by 32%. Some 22% said they were unsure.

Morning Consult, which conducts polls nationwide, surveyed Utah voters at a time when Romney was raising concern about Trump’s dealings with Ukraine.

The Utah senator, who during his year in office has been supportive and also critical of Trump, said Trump’s phone call with the new Ukrainian president, Volodymyr Zelenskiy, was “troubling in the extreme.” A memo about that call shows Trump asking for a “favor” from the country to investigate a conspiracy about Democrats and also former Vice President Joe Biden and his son Hunter.

Trump at the time was holding back hundreds of millions of dollars in military and State Department aid to Ukraine, a move that is now at the center of the impeachment trial that will begin in earnest in the Senate on Tuesday.

Romney, a former Republican presidential nominee, is now one of a few GOP senators who say they would like to hear from witnesses in the Senate trial or at least aren’t set on a quicker process than Senate Majority Leader Mitch McConnell of Kentucky plans.

Meanwhile, an anti-Trump Republican group will air ads in Utah encouraging Romney to continue his support for witnesses as part of a $1 million TV, billboard and online campaign targeting vulnerable Republicans — and Romney, who is seen as a key vote to push the Senate to hear from witnesses.

While Chief Justice John Roberts presides over the impeachment trial as prescribed by the Constitution, a majority of senators controls the rules of the proceedings. Democrats, and two independents that caucus with them, control 47 seats and need only four votes to override the GOP majority.

Romney has said he would vote against immediately dismissing the charges Trump faces and supports a move, after opening arguments, to allow witnesses. Bolton, a key witness to the Ukrainian dealings, has said he would testify if subpoenaed.

“Romney is doing the right thing by supporting the testimony of Bolton, and we want his constituents and GOP colleagues to know it's the right thing, so we're continuing to promote this message,” said Carson Putnam, spokesman for the group Republicans for the Rule of Law, which includes conservative pundit Bill Kristol.

Putnam added that while some Republicans are staking out positions like Romney, the White House is pressuring GOP senators and the group wants to make sure Romney gets the support he needs.

“We want to let them know that there are still Republicans out there – more than is typically acknowledged, and more than the White House would like to admit – who expect our leaders to lead, to maintain the integrity of the Senate, and to stand for the rule of law,” Putnam said.

The group plans to unveil a billboard in Salt Lake City next week as the Senate trial begins.

Kristol, who founded the now-defunct Weekly Standard, said in a statement that the Constitution gives the Senate the “sole power” to try impeachments.

“But the Senate can’t try an impeachment without a trial, and there’s no such thing as a trial without evidence,” Kristol said.