The effects of Mr. Trump’s victory are only beginning to be felt. But one of the biggest changes is playing out in abortion politics. From the composition of the Supreme Court (Mr. Trump has promised to nominate staunchly anti-abortion justices), to efforts on Capitol Hill to enact a permanent ban on taxpayer-financed abortions, to emboldened Republican statehouses like the one in Ohio, combatants on both sides see legalized abortion imperiled as it has not been for decades.

That includes, they agree, the possibility of overturning Roe v. Wade, the landmark 1973 abortion decision, during the Trump presidency.

“This is the strongest the pro-life movement has been since 1973,” said Marjorie Dannenfelser, the president of the Susan B. Anthony List, an anti-abortion group, and the chairwoman of a coalition of abortion opponents that worked to elect Mr. Trump. “We are dealing now with a president who has not been playing the game in the way that other presidents, including Republicans, have.”

Mr. Trump was elected after a decade of anti-abortion gains in state legislatures; Ohio is the 18th state to adopt a 20-week abortion ban, though two such bills, in Arizona and Idaho, did not survive constitutional challenges in federal court. States that preserve rights, like New York and California, are increasingly rare.

“I think we are standing on the precipice of a really dark time,” said Ilyse Hogue, the president of Naral Pro-Choice America. She said that Mr. Trump had “zero mandate” to roll back Roe, and that her group would fight back hard; its fund-raising and membership are up.