With the news that President Donald Trump has interviewed four anti-choice judges as potential nominees to succeed Justice Anthony Kennedy on the U.S. Supreme Court, women's rights advocates are turning their attention to Sen. Susan Collins, putting pressure on the so-called "moderate" Republican from Maine  to vote against any nominee who does not support access to abortion care and to defend Roe vs. Wade.

NARAL Pro-Choice America announced Tuesday that it had purchased full-page ads in four newspapers in Maine as well as ad space on the publications' websites.

"Trump has been loud and clear in saying he'd pick Supreme Court Justices to end Roe v. Wade," reads the ad. "We believe him. Don't you, Senator Collins?"

"Donald Trump has been crystal clear. He has a litmus test for his Supreme Court nominee: end Roe v. Wade. He said it repeatedly during his campaign. We believe him. For the sake of women in Maine, and across the country, we hope Senator Collins does too," NARAL President Ilyse Hogue said in a statement.

Collins has equivocated regarding whether she would vote to confirm a Trump nominee who was anti-choice—as many of the 25 who are considered contenders are.

"I'm going to have an in-depth discussion with the nominee and I believe very much that Roe v. Wade is settled law, as it has been described by Chief Justice Roberts. It has been established as a constitutional right for…45 years and was reaffirmed 26 years ago," Collins told ABC on Sunday. Last week she also described Roe as "settled law" to CBS, declining to say whether she would protect the law by voting against a judge who aims to overturn it.

Also on Sunday she told CNN, "I would not support a nominee who demonstrated hostility to Roe v. Wade because that would mean to me that their judicial philosophy did not include a respect for established decisions, established law."

NARAL and other pro-choice groups are demanding that Collins recognize the danger of confirming a nominee who, like Judge William Pryor, has called Roe vs. Wade "the worst abomination of constitutional law in our history" or Judge Amy Coney Barrett, who has called it an "erroneous decision."

Should all Democrats vote against a Trump nominee, Republicans will only be able to afford to lose one vote. Pro-choice groups are targeting Sen. Lisa Murkowski (R-Alaska) as well as Collins.

"The burden of proof is on the nominee to prove that they will proactively protect Roe v. Wade and until they do no senator, and particularly no senators who consider themselves pro-choice, should vote for the nominee. Too much is on the line to not believe Donald Trump will do exactly what he said he'd do," Hogue said.

The Portland Press Herald, the Bangor Daily News, the Lewiston Sun Journal, and the Kennebec Journal/Morning Sentinel will all run NARAL's ad both in their print editions and online. It will also appear in Google and Twitter searches.

Meanwhile, pro-choice Americans have begun sending coat hangers in bulk to Collins's offices—a grim reminder of one method women used to perform dangerous, illegal abortions before the Supreme Court passed Roe vs. Wade in 1973.

Multiple polls have found that most Americans do not believe Roe vs. Wade should be overturned, unlike Trump's nominees. A Quinnipiac University poll released Monday found that 63 percent agreed with the decision, while the Kaiser Family Foundation showed last weekthat 67 percent wanted the ruling to stand.