Pro-choice activists are relying on GOP Sens. Susan Collins and Lisa Murkowski to vote against President Donald Trump's nominee to replace Justice Anthony Kennedy on the Supreme Court.

Trump promised to nominate pro-life judges during his campaign, which concerns activists that Roe v. Wade could be overturned.

Legal and constitutional experts, however, say that the landmark case is unlikely to be overturned.

Republican Sens. Susan Collins of Maine and Lisa Murkowski of Alaska made headlines last summer when they defied their party and president in voting against the repeal of the Affordable Care Act.

Now, they are being looked to as critical votes in the confirmation process for President Donald Trump's nominee to fill the seat on the Supreme Court vacated by Justice Anthony Kennedy's retirement, and advocates are hoping they will vote against anti-abortion nominees.

Kennedy delivered critical votes in several key cases concerning abortion rights. He co-wrote the majority opinion to uphold large parts of Roe v. Wade in the 1992 case Casey v. Planned Parenthood and overturned Texas restrictions on abortion clinics in Whole Woman's Health v. Hellerstedt last year.

Kennedy's vacancy gives an opening for Trump to satisfy his base in a crucial election year. During his presidential campaign, Trump vowed to appoint federal judges who were pro-life and supported overturning Roe v. Wade. the landmark 1973 Supreme Court case that established a right to abortion on a federal level.

This will be Trump's second nomination of a Supreme Court justice. In January 2017, he nominated current Associate Justice Neil M. Gorsuch to fill the seat vacated by Antonin Scalia's death.

Ilyse Hogue, the President of NARAL Pro-Choice America, told reporters on Thursday that Trump's efforts should not be under-estimated.

"He is dedicated to overturning Roe v. Wade, criminalizing abortion, and punishing women. We took him at his word then and we take him at his word now," she said. "This is not a drill. The laws criminalizing abortion and certain kinds of contraception are moving through the courts."

Collins told reporters on Wednesday that she views Roe v. Wade "as being settled law."

"It's clearly precedent," she said. "I always look for judges who respect precedent."

But Ezra Levin, co-founder of progressive group Indivisible, said "a vote for any of the proposed nominees on Trump’s list is a vote to overturn Roe."

"She cannot simultaneously say she supports Roe v. Wade and vote for any of Trump's nominees," he said. "She would be trying to have it both ways, and it would be frankly quite hypocritical."

Murkowski did not directly address the issue of abortion, but said in a statement posted to Twitter that she would "carefully scrutinize the qualifications of judicial nominees" and "cast an independent vote."

Both Hogue and Dawn Laguens, executive vice-president of Planned Parenthood, said GOP senators from states with an "independent streak" such as Maine, Alaska, and New Hampshire could likely vote against Trump's nominees. Progressive grassroots organizers are carrying out a "50-state strategy" to lobby all members of the Senate to vote against Trump's nominees.

Citing polling showing that the vast majority of Democrats and independents support Roe v. Wade, Hogue said "aanyone up for election in 2018 should be quite frightened" about voting for a nominee who opposes Roe.

This may put red-state Democratic senators up for election this year, some of whom represent large pro-life constituencies, in a tough position.

What the experts say

While abortion-rights advocates have sounded the alarm on the prospects of one of Trump's nominees overturning Roe, legal and constitutional experts say that while Trump's nominee will likely be conservative on abortion, fears of Roe being overturned are misplaced.

Carrie Severino, chief counsel of the Judicial Crisis Network and an expert on judicial nominations, was skeptical that Collins and Murkowski would vote against any one of Trump's proposed nominees on that basis.

"Given the individuals on his list, these are some of the best and the brightest of our legal stars and judges today. I think all of them will be very much like Gorsuch," Severino told Business Insider on Thursday. "Both Collins and Murkowski voted for Gorsuch, were pleased with Gorsuch, and will be pleased to vote for someone else like him.”

Severino added that the court will likely handle abortion cases "the same way they've been handled up until now," and said the worries of Roe v. Wade being overturned are a commonly-used form of "scaremongering" against conservative judicial nominees. She noted that only one justice currently on the court, Clarence Thomas, would likely support overturning Roe.

"I do not think it particularly likely that Roe (and Casey) are likely to be overturned based on this one appointment," said Glenn Cohen, a professor at Harvard Law School and a constitutional expert. "I find it hard to think that [Chief Justice] Roberts — who has a more long-term view of the arc of the court and a desire to preserve its institutional role — would facially overrule Roe."