Sen. Susan Collins (R-ME), a key swing vote on President Donald Trump’s Supreme Court nominee, said on Sunday that she would oppose any individual who would overturn the landmark Roe v. Wade decision.

“A candidate for this important position who would overturn Roe v. Wade would not be acceptable to me because that would indicate an activist agenda that I don’t want to see a judge have,” Collins said on ABC’s This Week. “And that would indicate to me a failure to respect precedent of fundamental tenet of our judicial system.”

The 1973 ruling legalized abortion nationwide, and has been a target of pro-life conservatives for decades. Collins is one of two pro-choice Republicans in the Senate. She, along with other senators who are considered to be swing votes in the upcoming confirmation battle, met with Trump at the White House last week to discuss the vacancy.

“I emphasized that I wanted a nominee who would respect precedent, a fundamental tenet of our judicial system,” Collins said in CNN’s State of the Union, adding that she asked the president to “broaden” his list of 25 possible nominees.

Trump is expected to soon name his nominee to replace Justice Anthony Kennedy, who announced last week that he would retire at the end of July after serving more than 30 years on the highest court.

Progressives have warned that Kennedy’s departure could lead to major restrictions on abortion rights and other issues that Democrats have championed in recent decades. Some Senate Democrats are urging Senate Majority Leader Mitch McConnell (R-KY) to delay the confirmation process until after the midterm elections, but McConnell has said that the Senate would consider Trump’s nominee in earnest.

Senate Democrats, meanwhile, have few—if any—procedural tools at their disposal to block or slow down the process. And some of the more conservative members of the Democratic caucus such as Sens. Joe Manchin (D-W.V.), Heidi Heitkamp (D-N.D.) and Joe Donnelly (D-IN) might once again break rank and vote for Trump’s nominee. Those three lawmakers, all of whom hail from states that Trump won in 2016 and are facing tough re-election battles this year, all voted to confirm Neil Gorsuch, Trump’s first Supreme Court nominee, last year.