Republican Senate candidate Roy Moore arrives on his horse to cast his ballot in Gallant, Ala., on Tuesday. (Carlo Allegri/Reuters)

Roy Moore’s campaign had one weapon that seemed to offer his supporters a counterweight to the allegations that he had pursued teenaged girls when he was in his 30s: abortion.

In the run-up to Tuesday’s special election for U.S. Senate, the Alabama Republican denied any improper sexual behavior but also went on the offensive against Democrat Doug Jones for being a pro-choice radical, a supporter of abortion at any time, for any reason.

Republican strategists believed that for Alabama’s antiabortion hardliners, a vote for Jones would be a bridge too far. They were wrong.

Jones’s unlikely victory, the first by a Democratic Senate candidate in Alabama in a quarter-century, was driven in part by revulsion over the allegations against Moore, but also by resistance against a torrent of TV ads that urged voters to make abortion a defining litmus test.

After she voted in the southern suburbs of Birmingham, Jennifer Greer, a 61-year-old business consultant, said she had tired of seeing TV spots arguing that conservatives should make their choice based on Moore’s antiabortion credentials.

“A lot of what you’re seeing with that conservative white church element is that they’re not informed,” said Greer, who voted for Jones. “How pro-life is not funding” health insurance for children? “They focus on one woman’s health procedure, and they make that the focus of the campaign.”

In the annals of the culture wars, abortion has long been a clear marker, an issue that packs an emotional wallop and lets both sides see themselves as occupying the moral high ground.

But Tuesday’s election added a new level of complexity to the abortion debate, pitting antiabortion supporters of Moore against those who believed that accusations of sexual misconduct disqualified him from elective office.

“In both cases, it’s about women’s sexuality, the sexual revolution and feminism,” said Leslie Reagan, a historian of the abortion battles who teaches at the University of Illinois. For both Moore voters and those who crossed over to support Jones, abortion became a useful shorthand, a way to place themselves on one or the other side of a national clash in world views.

Jones’s victory demonstrated once again that even in the conservative Deep South, abortion has become an accepted, if still controversial, practice. Southerners have abortions at about the same rate as do women in the rest of the country, and Southerners have rejected some efforts to move toward a hard ban on the procedure.

In 2011, Mississippi voters overwhelmingly rejected a proposed constitutional amendment that would have declared that life begins at fertilization. Planned Parenthood and medical societies argued that such a declaration would undermine access to infertility treatments.

“There’s a lot more going on in the South than people may think,” Reagan said.

Preliminary exit poll results: How different groups voted in Alabama

Many on the right thought that voters with a long history of supporting traditional values would put Moore over the top. “Abortion is a galvanizing issue in Alabama,” said Matt Barber, general counsel of Christian Civil Rights Watch, a conservative legal group, and a former dean at Liberty University. “President Obama said the social issues were so ’90s, but in flyover country, the desire not to be complicit in abortion homicide remains one of the top concerns.”

Barber said the abortion debate brings Trump voters together because it signals a moral standard for people who believe that “people in government, the media, academia, entertainment and the halls of Congress are trying to re-create America in their secular, Euro-socialist image. The nation is divided between two incompatible worldviews. We don’t see minds being changed. There is no political solution. The only solution is a spiritual one, a Christian revival.”

And some voters did see it that way. At a Moore rally in Midland City on the eve of the vote, Jack Reynolds, a 63-year-old who lives on a farm in Alabama’s southeast corner, said he stuck with Moore because “He’s defending . . . our core values about love of life.” Reynolds said he doesn’t expect abortion to become illegal again, but “I just love the unborn far too much to ever vote for a national Democrat.”

For many conservative voters, abortion is a core identifier, a way to show that they are part of Trump’s “forgotten men and women.”

But although conservative Christians were an essential element of Trump’s winning coalition last year, the focus on abortion in Moore’s campaign was apparently not sufficient to motivate Trump voters to take part in an unusual mid-December special election.

Moore’s campaign injected the issue into the race as a time-tested way of painting Democrats as extremists, said Drew Halfmann, a sociologist at the University of California at Davis who focuses on the politics of abortion.

“The Republicans used abortion as a very effective signaling device,” Halfmann said. “For a time, they used same-sex marriage to keep the pot boiling but now that that controversy has been resolved, they’re back to abortion.”

The tactic had worked in the past. "This outsider sensibility has been a real vote-getter, from 1970, when Time magazine declared Middle Americans 'Man and Woman of the Year,' to Trump's election and Moore's support," said Stacie Taranto, a historian at Ramapo University who studies the abortion debate.

But most Alabama voters did not put abortion atop their list of defining issues, according to a Washington Post-Schar School poll in late November. The survey found that 41 percent of voters thought a candidate's views on health care were most important, followed by moral conduct at 26 percent. Abortion trailed well behind at 14 percent.

Abortion remains one of the few issues that most voters call an absolute litmus test; that is, along with health care, same-sex marriage and immigration, abortion is a rare issue on which a majority of voters say they could not bring themselves to vote for a candidate who disagrees with them.

But in Tuesday’s vote, many did exactly that — an indication, some scholars said, that as Americans, even in the Deep South, become more secular, abortion politics no longer wields the same sway it once did.

Moore’s campaign injected the issue into the campaign, arguing in TV ads and speeches that Jones favored “full-term abortions.” Jones did say in a September TV appearance that he supported “late-term abortions . . . if pregnancy threatens the health of the mother,” but he subsequently said he opposed such procedures.

For many Christian conservatives, the sense of being on the wrong side of the law of the land on abortion’s legality fed a growing sense of feeling disrespected or excluded from the mainstream. Being antiabortion has become part of the emerging identity politics of the right, as expressed in the nationalist, populist appeal that Trump and his former chief strategist, Stephen K. Bannon, crafted in last year’s campaign.

The nation’s divide over abortion has remained relatively stable through recent decades. Support for the idea that abortions should be legally available to women for any reason has remained within a few points of 40 percent of Americans for more than 30 years, and support for keeping abortion legal if a woman’s health is seriously endangered has remained above 80 percent for nearly half a century, according to the General Social Survey, which has studied Americans’ perspectives since 1972.

But there's been no such stability when it comes to how attitudes on abortion line up with Americans' political affiliation. From the late 1970s through the early 1980s, Democrats and Republicans were equally likely to say they supported women's rights to an abortion for any cause. It was only in 1998 that the percentage of Republicans supporting abortion collapsed, remaining at or below 30 percent ever since. And it wasn't until this decade that a majority of Democrats embraced that stand.

From the start of the abortion reform movement in the 1960s until at least Ronald Reagan’s 1980 campaign, many Republicans were pro abortion rights, seeing legalized abortion as an expression of individual rights and therefore a traditionally GOP issue, Taranto said.

“Abortion and family values weren’t political issues until the modern women’s movement made the personal political,” she said.

Only in the 1980s did a conservative backlash over feminism persuade many GOP politicians that there was a strategic advantage to joining abortion and family values to law and order and anti-communism as core elements of what it meant to be a Republican.

“In the ’70s, the focus on abortion and homosexuality brought together groups that previously despised each other — evangelicals, Mormons and Catholics,” Leslie Reagan said.

David Weigel in Birmingham, Jenna Johnson in Dothan, Ala., and Scott Clement contributed to this report.