Amidst all the talk about the impact of a likely reversal of Roe v. Wade by the Supreme Court’s conservative majority, I thought a history lesson was in order, so I wrote one at New York:

Last week, the Women’s Health Protection Act, which would have codified abortion rights, died in in the Senate by a vote of 51 to 49. All 210 House Republicans and all 50 Senate Republicans voted against the legislation. This surprised no one, but it’s actually odd in several ways. While Republican elected officials are almost monolithically opposed to abortion rights, pro-choice Republican voters didn’t entirely cease to exist, and this could become a problem for the party if, as expected, the U.S. Supreme Court strikes down the right to abortion at the end of this term.

Though polling on the issue is notoriously slippery, our best guess is that a little over a third of Republicans disagree with their party on whether to outlaw abortion (while about one-quarter of Democrats disagree with their party on the topic). These Americans have virtually no representation in Congress with the limited exceptions of Senators Susan Collins and Lisa Murkowski (both GOP senators support some abortion rights, but they are still opposed the WHPA and are against dropping the filibuster to preserve abortion rights).

Ironically, abortion rights as we know them are, to a considerable extent, the product of Republican lawmaking at every level of government. The most obvious examples are the two Supreme Court decisions that established and reaffirmed a constitutional right to abortion. Of the seven justices who supported Roe v. Wade, the 1973 decision that struck down pre-viability-abortion bans, five were appointed by Republican presidents, including the author of the majority opinion, Harry Blackmun, and then–Chief Justice Warren Burger. All five justices who voted to confirm the constitutional right to pre-viability abortions in 1992’s Planned Parenthood v. Casey were appointed by Republican presidents as well.

These pro-choice Republicans weren’t just rogue jurists (though their alleged perfidy has become a deep grievance in the anti-abortion movement). Today’s lock-step opposition to abortion rights among GOP elected officials took a long time to develop. Indeed, before Roe, Republicans were more likely to favor legal abortion than Democrats. In New York and Washington, two of the four states that fully legalized pre-viability abortions in 1970, Republican governors Nelson Rockefeller and Daniel Evans were at the forefront of abortion-rights efforts. They weren’t fringe figures; Rockefeller went on to become vice-president of the United States under Gerald Ford. Pre-Roe, various other Republican officials supported more modest efforts to ease abortion bans; among them was then–California governor Ronald Reagan, who signed a bill significantly liberalizing exceptions to an abortion ban in 1967.

The anti-abortion movement’s strength in the Republican Party grew steadily after Roe in part because of a more general ideological sorting out of the two major parties as liberals drifted into the Democratic Party and conservatives were drawn into the GOP. To put it another way, there has always been ideological polarization in American politics, but only in recent decades has it been reflected in parallel party polarization. But that doesn’t fully explain the GOP’s shift on abortion policy.

Beginning in 1972 with Richard Nixon’s reelection campaign, Republicans began actively trying to recruit historically Democratic Roman Catholic voters. Soon thereafter, they started working to mobilize conservative Evangelical voters. This effort coincided with the Evangelicals’ conversion into strident abortion opponents, though they were generally in favor of the modest liberalization of abortion laws until the late 1970s. All these trends culminated in the adoption of a militantly anti-abortion platform plank in the 1980 Republican National Convention that nominated Reagan for president. The Gipper said he regretted his earlier openness to relaxed abortion laws. Reagan’s strongest intraparty rival was George H.W. Bush, the scion of a family with a powerful multigenerational connection to Planned Parenthood. He found it expedient to renounce any support for abortion rights before launching his campaign.

Still, there remained a significant pro-choice faction among Republican elected officials until quite recently. In 1992, the year Republican Supreme Court appointees saved abortion rights in Casey, there was a healthy number of pro-choice Republicans serving in the Senate: Ted Stevens of Alaska, John Seymour of California, Nancy Kassebaum of Kansas, William Cohen of Maine, Bob Packwood of Oregon, Arlen Specter of Pennsylvania, John Chafee of Rhode Island, Jim Jeffords of Vermont, John Warner of Virginia, and Alan Simpson and Malcolm Wallop of Wyoming. Another, John Heinz of Pennsylvania, had recently died.

Partisan polarization on abortion (which, of course, was taking place among Democrats as well) has been slow but steady, as Aaron Blake of the Washington Post recently observed:

“In a 1997 study, Carnegie Mellon University professor Greg D. Adams sought to track abortion votes in Congress over time. His finding: In the Senate, there was almost no daylight between the two parties in 1973, with both parties voting for ‘pro-choice’ positions about 40 percent of the time.

“But that quickly changed.

“There was more of a difference in the House in 1973, with Republicans significantly more opposed to abortion rights than both House Democrats and senators of both parties. But there, too, the gap soon widened.

“Including votes in both chambers, Adams found that a 22 percentage- point gap between the two parties’ votes in 1973 expanded to nearly 65 points two decades later, after Casey was decided.”

By 2018, every pro-choice House Republican had been defeated or had retired. The rigidity of the party line on abortion was perhaps best reflected in late 2019, when a House Democrat with a record of strong support for abortion rights, Jeff Van Drew of New Jersey, switched parties. Almost instantly, Van Drew switched sides on reproductive rights and was hailed by the hard-core anti-abortion Susan B. Anthony List for voting “consistently to defend the lives of the unborn and infants.”

With the 2020 primary loss by Illinois Democratic representative Dan Lipinski, a staunch opponent of abortion rights, there’s now just one House member whose abortion stance is out of step with his party: Texas Democrat Henry Cuellar, who is very vulnerable to defeat in a May 24 runoff.

If the Supreme Court does fully reverse Roe in the coming weeks, making abortion a more highly salient 2022 campaign issue, the one-third of pro-choice Republican voters may take issue with their lack of congressional representation. Will the first big threat to abortion rights in nearly a half-century make them change their priorities? Or will they still care more about party loyalty and issues like inflation? Perhaps nothing will change for most of these voters. But in close races, the abandoned tradition of pro-choice Republicanism could make a comeback to the detriment of the GOP’s ambitious plans for major midterm gains.