Supreme Court Justice Anthony Kennedy’s retirement could pave the way for major changes in women’s health and abortion issues, possibly some of the biggest since the 1973 landmark case Roe v. Wade, if the Senate confirms a conservative justice.

Kennedy has been a key swing vote on women’s health issues. Two years ago, he joined the plurality in Whole Woman’s Health v. Hellerstedt, a major abortion rights case, which struck down a Texas law that would have resulted in the closure of most of the state’s abortion clinics.

In 1992, in Planned Parenthood v. Casey, he joined the plurality in reaffirming the Roe decision while allowing states to regulate the procedure unless it imposes an “undue burden” on women’s right to access abortion. The decision differed from Roe by allowing state regulation on abortions to take place in the first trimester.

This week, Kennedy sided with the conservative justices in National Institute of Family and Life Advocates v. Becerra, a free speech case challenging a California state law. It required licensed crisis pregnancy centers to post notices explaining that the state offers subsidized family planning services, including abortion, and required unlicensed centers to disclose that they do not have medical personnel on staff. The opinion said the pregnancy centers “are likely to succeed” in a constitutional challenge to the restrictions involving licensed centers.

Overturning Roe v. Wade, which guarantees a woman’s legal right to abortion, has been a goal of many anti-abortion groups since the ruling was issued. Momentum picked up after President Donald Trump, backed by a Republican-controlled Congress, was elected.

“As you all know, Roe vs. Wade has resulted in some of the most permissive abortion laws anywhere in the world,” Trump said during the annual March for Life event earlier this year.

Trump said on Wednesday after Kennedy’s announcement that the search will “begin immediately” and come from the previously established list from which he selected Justice Neil Gorsuch.

“Justice Kennedy was critical to the survival of Roe. If Trump appoints another Gorsuch, as seems likely now, I fear that Roe will be quickly overruled,” said Geoffrey R. Stone, a law professor at the University of Chicago who filed an amicus brief in Whole Woman’s Health v. Hellerstedt.

Watch: Gorsuch’s Swearing-In Ceremony at the White House

“Justice Kennedy’s retirement upsets a delicate balance and puts more than women’s access to abortion care at great risk. A woman’s ability to make her own health care decisions — of all kinds — will be restricted if Roe vs. Wade is overturned,” said Susan Wood, professor of health policy and environmental and occupational health and the director of the Jacobs Institute of Women’s Health at George Washington University.

She mentioned the possibility of other court cases on the 2010 health care law, which she said “will have profound impacts on the health of us all, and the next justice will also will be critical to the outcome.”

Not everyone thinks that Kennedy’s retirement will have such a quick and far-reaching impact.

Elizabeth Slattery, a legal fellow with the conservative Heritage Foundation, thinks any changes to health care will come slowly.

“I certainly don’t think that Roe v. Wade will be overturned in the next term,” said Slattery, who said cases generally take time to reach the Supreme Court from the lower courts. “Your average case takes some time to get to the court.”

She said the same is likely for any possible changes to the 2010 health care law. “My inclination is that if there are changes to the Affordable Care Act, they are not going to be from the Supreme Court but from Congress,” she said.

Congress fell short in its efforts last year to repeal most of the law but did eliminate the penalty that most Americans have to pay if they do not get health care coverage.

Congressional reaction

Majority Leader Mitch McConnell of Kentucky said on the Senate floor that a confirmation vote would happen this fall. Some Democrats such as Senate Health, Education, Labor and Pensions ranking member Patty Murray, a strong advocate for abortion rights, said that McConnell should wait until after the midterm elections.

“As Sen. McConnell has said in the past, we should hear what the voters have to say,” the Washington Democrat said.

“The Senate should reject on a bipartisan basis any justice who would overturn Roe v. Wade or undermine key health care protections,” said Minority Leader Charles E. Schumer.

A nominee would need 51 votes, possibly including one from Vice President Mike Pence, and both sides are likely to campaign on this issue in an effort to secure the Senate majority.

“We will not stop fighting to elect pro-choice Democratic women to the Senate who will defend women’s access to safe, legal abortion and other forms of critical reproductive health care and fight for the rights of all Americans,” said Stephanie Schriock, president of EMILY’s List, which endorses candidates who support abortion rights.

“The future of the Supreme Court is now fully in play. Senator Heller wants you to vote for him because he’ll rubber stamp another nominee from President Trump, who could jeopardize Roe v. Wade and undermine coverage protections for pre-existing conditions,” tweeted Jacky Rosen, a Democrat challenging Sen. Dean Heller in Nevada this fall.

Heller sent out a fundraiser letter on the news of Kennedy’s retirement around the same time.

Interest groups

Groups such as the conservative Susan B. Anthony List have pushed for Trump to only consider anti-abortion candidates and rallied grassroots support for Gorsuch before his confirmation.

“Justice Kennedy’s retirement from the Supreme Court marks a pivotal moment for the fight to ensure every unborn child is welcomed and protected under the law,” said the group’s president Marjorie Dannenfelser. “The most important commitment that President Trump has made to the pro-life movement has been his promise to nominate only pro-life judges to the Supreme Court, a commitment he honored by swiftly nominating Judge Neil Gorsuch.”

“The list of potential nominees includes men and women who are similarly qualified, exhibit the qualities necessary to sit on the Supreme Court and, most importantly, who interpret the Constitution as it was originally written,” said Jeanne Mancini, president of March for Life.

Numerous abortion rights groups echoed the sentiment that conservatives’ goal would be to overturn Roe.

“The stakes of the coming nomination fight are extraordinary. The future of reproductive rights is on the line. It’s up to the Senate to ensure that Anthony Kennedy be replaced with a justice who will affirm the fundamental rights of all,” said Nancy Northup, president of the Center for Reproductive Rights.

Senate Judiciary Chairman Charles E. Grassley of Iowa suggested he would not wait until after the November elections to consider the nomination of a replacement. Moderate Republican Sen. Susan Collins of Maine told reporters that she did not see a need to delay a vote until after the election.

Niels Lesniewski contributed to this story.