“Trump did this,” the campaign ads for Kamala Harris declare.

“This” was appointing three Supreme Court justices who helped overturn Roe v. Wade, paving the way for the state abortion bans that have led to often harrowing experiences for many pregnant women denied care.

As seismic as that was, activists on both sides of the debate believe a newly elected President Donald J. Trump could go further to effectively ban abortion nationwide — and abortion opponents have given him the road map.

It is hard to know what on the anti-abortion agenda Mr. Trump would support. He has shifted his public views on abortion so often that it’s hard to say what he believes or wants to do. He has said he wants to “leave it to the states.” More recently, he said he would not sign a federal abortion ban, and would veto one if a Republican-controlled Congress sent it to his desk. He has publicly supported I.V.F., which some anti-abortion groups oppose.

But Mr. Trump would also be under pressure from the anti-abortion groups that have ardently supported him to take other actions that would go much further than the 15-week national bans that congressional Republicans have proposed since Roe was overturned. These include reversing federal guidance that says even states with bans must allow doctors to provide abortion in cases of medical emergency; using administrative agencies to ban abortion pills; and using his executive powers to achieve the anti-abortion movement’s ultimate goal: recognizing fetal personhood in the Constitution.

Those actions would not require cooperation from Congress, and could play out in the far reaches of the federal bureaucracy by Trump appointees. While any changes would almost certainly be challenged in court, the judges who hear those cases could be Trump appointees, existing or new.

“There are levers that he and his appointees can pull, way short of an abortion ban, which would make abortion much more difficult — if not illegal — in all the states where it’s legal still,” said David S. Cohen, a law professor at Drexel University who has written extensively about federal regulation of abortion.