With the Supreme Court now looking likely to weaken or overturn the landmark Roe v. Wade decision on abortion, activists and both political parties are bracing for a new battle over one of the country’s longest-running cultural divides.

State lawmakers, not Supreme Court justices, would largely hold the decision-making power over abortion and determine the ease or difficulty of obtaining one. Many legislators would be forced to argue over the most intimate details of transvaginal sonograms, conception and when exactly life begins. Newer issues, like fights over telemedicine and abortion pills, could gain fresh political momentum, as patients seek out ways to circumvent restrictions by managing their own abortions.

In the aftermath of the oral arguments at the Supreme Court on Wednesday in the Mississippi case, both sides appeared to agree on at least one thing.

“This could be an important point, a seismic shift in the politics of this issue,” said Marjorie Dannenfelser, president of the Susan B. Anthony List, which supports anti-abortion candidates and campaigns against abortion rights supporters in races across the country.

A decision by the Supreme Court is likely to come in June or July, months before the midterm elections that will determine control of Congress and the future of President Biden’s agenda.

The outcome the justices signaled during questioning on Wednesday — a curtailing of the constitutional protections for abortion established under Roe v. Wade, if not an outright dismantling of that standard — would spur a reckoning for abortion rights advocates.

Democrats are worried that they may soon face a more urgent state-by-state fight to preserve as many protections as they can, and they are planning new drives to take control of statehouses. Many believe they were already on the defensive, given the conservative majority on the Supreme Court and the flood of restrictions that have passed in state legislatures. Some activists said winning back those rights would most likely require a decades-long campaign.

“We have to begin to help people to understand what it is going to take to win back this issue,” said Destiny Lopez, a co-president of All* Above All, an abortion rights group. “We are in for another long fight. God help me if it’s another 50 years. At minimum, it’s another 15, 20 years.”

For opponents of abortion, a win at the Supreme Court would be the fulfillment of decades of work to curb abortion rights from statehouses to the White House. Activists said that while there would be plenty to push for on a policy level — restricting access to abortion-inducing medication online, funding more services for women who face unwanted pregnancies — they also acknowledged that a degree of complacency could set in.

“There are going to be those who claim victory and walk away,” said Tom McClusky, president of March for Life Action, which lobbies against abortion. “Most donors want to fund a fight. They want to fund warriors, not Samaritans.”

But Mr. McClusky added that he and other activists still see their cause as a long-term struggle to change public perceptions about abortion.

“We want to build a culture where abortion is unthinkable,” he said. “So even if by some miracle next spring Roe is overturned, there is still going to be a ton of work to do.”

In interviews, activists on both sides said they envisioned fights that would look very different depending on the state.

In California, New York and other overwhelmingly Democratic states, abortion rights supporters are expected to push for expanding access to abortion, leveraging new technologies like telehealth, improving insurance coverage of the procedure and creating new funds to cover costs for women traveling out of state. But in places like Alabama, conservatives are expected to push for new legislation and policies aimed at closing any loopholes that would still make abortion possible while also strengthening support for women who face an unexpected pregnancy.

Mini Timmaraju, president of NARAL Pro-Choice America, one of the most prominent abortion rights organizations, said her group hoped to move the Democratic Party into a more aggressive position, starting with plans to intensify the pressure on Congress and political candidates to support a bill to enshrine abortion rights into federal law. Such a measure passed the House in September but stands little chance of becoming law under current legislative rules.

They also plan to use the issue as a cudgel in the midterm elections, arguing that a bigger Democratic majority in Congress is needed to protect access to the procedure and seat judges who are not hostile to abortion rights.

“Everything is on the table after this — constitutional amendments, ballot initiatives, expanding the court,” Ms. Timmaraju said. “For so long we’ve been on the receiving end of these fights. We’ve been triaging, triaging and triaging, and now we have to take a step back and think what is the long-term agenda.”

Some Democrats and supporters of abortion rights would most likely step up their pressure on Mr. Biden, who has a long and complicated record on the topic and hasn’t yet spoken the word abortion as president, according to activists who track the issue.

But other abortion rights activists argue that their movement’s focus on the federal level has led them to the cusp of a defeat they fear is already well underway. Some worry that the disconnect over what will likely remain legal in blue states and be banned in red states could make it hard to galvanize liberals, who tend to be concentrated in states where abortion access will be guaranteed.

Many activists want to place more focus on flipping state legislatures, arguing that they should model their effort on the work of the social conservatives on the other side of the issue. Those conservative efforts reached new heights this year, when states enacted 106 abortion restrictions, the highest number of restrictions passed since Roewas decided in 1973, according to the Guttmacher Institute, a liberal group that tracks women’s reproductive health legislation.

“We’re already living in a post-Roe world,” said Ms. Lopez with the All* Above All abortion rights group.

If the Supreme Court overturns Roe, 26 states are certain or likely to ban legal abortion, according to the Guttmacher Institute, through laws banning abortion that were enacted before Roe but remain on the books, so-called trigger bans that would take effect automatically or by quick state action if Roe no longer applies and laws that prohibit abortion after about six weeks of pregnancy.

Republican-led states are expected to take a hard look at how women might try to get around such bans. Some already have, giving anti-abortion activists a template.

In Texas, for instance, a law that took effect on Thursday prohibits physicians and other suppliers of medication from mailing abortion-inducing pills to women. The state also requires a clinician to be present when dispensing such medication, as do 18 others, banning the increasingly popular option of telemedicine for women seeking to terminate a pregnancy.

Abortion pills have become the most common method used for abortions up to 10 weeks’ gestation. Many expect they would only become more widely used if Roe is overturned. “Looking ahead, this is one of our biggest areas of concern,” said Katie Glenn, government affairs counsel for Americans United for Life.

States could also quickly move to pass or enforce copycat laws similar to the Mississippi law being debated by the court that ban the procedure after 15 weeks of pregnancy.

Abortion opponents said those policy fights would be an opportunity for them to learn who their true allies are. Politicians who have voted for restrictive measures in the past, but only because they knew they would never become law, may no longer have that option.

“If Roe is hobbled or overturned, and there is a restoration of states’ abilities to pass laws on abortion, then it’s not hypothetical anymore,” Ms. Dannenfelser of the Susan B. Anthony List said.

Abortion rights advocates, meanwhile, are building financial, medical and volunteer resources to help people travel across state lines to receive the procedure, with the expectation that many trips would most likely require a plane flight. Maps are being drawn up of “haven states,” “middle ground” and “at risk” areas.

Abortion funds around the country — largely volunteer-run nonprofits that help those seeking abortions by paying for travel, pills and procedures — dispensed $9.4 million in 2020, an increase from $4 million in 2017, according to the National Network of Abortion Funds.

Texas provides a preview of what the national landscape could become.

A new law there bans abortions after about six weeks. Clinics in surrounding states have been inundated with patients, procedures have become more expensive and women who cannot afford to travel have been forced to carry their pregnancies. The influx of patients from Texas created a domino effect in neighboring states, decreasing the availability of appointments and pushing some residents to also travel out of state for care.

“Basically, if you’re in the South, you’re looking at Illinois, Virginia — maybe — and Colorado. We’re talking really far traveling for people,” said Amy Hagstrom Miller, the president of Whole Woman’s Health, which operates abortion clinics in Texas and three other states.