Brett M. Kavanaugh, President Trump's Supreme Court nominee, listens to senators make their opening statements Tuesday during his confirmation hearing. (Melina Mara/The Washington Post)

Brett M. Kavanaugh’s confirmation hearing is a triumphant moment for both the Republican Party and its social movement allies, especially antiabortion organizations. For years, these groups have built a strategic alliance with the GOP. This partnership centers on activists’ hope that Republican presidents would nominate Supreme Court justices who would overturn Roe v. Wade. After the first day of Kavanaugh’s hearings, the marriage between the Republican Party and the antiabortion movement seems closer than ever.

But if a post-Kavanaugh court overturns Roe, this alliance could fracture, costing the GOP the loyalty of antiabortion voters.

When the Supreme Court decided Roe v. Wade in 1973, the antiabortion movement was politically diverse. Some abortion opponents were conservatives who saw Roe as an example of the problems with big government. Others defined themselves as Democrats and favored a more generous welfare state, viewing Roe as an example of the sort of civil rights violation that liberals traditionally tried to remedy.

Initially, these advocates primarily pushed a constitutional amendment banning abortion coast to coast. After all, overturning Roe — which seemed extremely unlikely in the mid-1970s — would only have allowed states to criminalize abortion, rather than requiring them to. Antiabortion advocates supported candidates, both Republican and Democrat, who backed their position.

In 1980, Ronald Reagan, the Republican presidential nominee, pledged strong support for a constitutional ban. The religious right also mobilized, offering a powerful ally for struggling antiabortion groups. The Democratic Party, by contrast, ran on a platform that endorsed Roe as the law of the land.

The Democrats’ position on reproductive health reflected the increasing influence of abortion rights supporters on the party’s agenda. To antiabortion groups, it increasingly seemed that the only way to amend the Constitution was to depend on the GOP.

By the mid-1980s, however, the most strategically sophisticated antiabortion groups had given up on amending the Constitution, at least in the short term. Sufficient public support simply didn’t exist, and Congress continued killing any amendment proposals that came up for consideration.

But rather than back away from their alliance with Republicans, antiabortion groups remained in lockstep with their political patrons. Why? Because leading organizations such as the National Right to Life Committee (NRLC) had embedded themselves in the Republican Party and used those political connections to raise money and exert influence. And they had a new primary focus: The groups argued that by remaining in the Republican coalition, abortion foes could influence Supreme Court nominations. With the right set of justices, Roe v. Wade could be overturned.

Since the 1980s, abortion opponents have sometimes second-guessed their alliance with the GOP. Absolutists have argued that the mainstream antiabortion movement has lost its ability to pressure the GOP, instead taking whatever crumbs Republican leaders will give them. Left-leaning abortion opponents have balked at efforts to tie opposition to abortion to broader conservative causes such as the fight against campaign finance restructuring.

At times, Republican leaders also questioned the partnership. In the late 1980s and early 1990s, Republican National Committee chairman Lee Atwater wondered whether opposition to abortion was hurting the GOP. Post-mortem analyses of presidential elections hinted that antiabortion positions sometimes cost the GOP votes.

But the coalition between abortion opponents and the GOP held. Republicans believed that a committed group of single-issue voters still could help win key races. Abortion foes, in turn, remained steadfast in their belief that Republican leaders could help them transform the Supreme Court. And in the meantime, party loyalty meant that members of groups such as the NRLC took key positions in Republican administrations and the Republican National Committee.

In 1992, new doubts emerged about the wisdom of relying on the GOP when the Supreme Court affirmed the right to abortion in Planned Parenthood v. Casey.

Casey made it easier for states to regulate abortion, but abortion opponents had expected much more.

After pledging to undo Roe, Reagan and his successor, George H.W. Bush, had chosen five of the court’s sitting justices — enough to undo abortion rights. Two of the other four justices had been extremely critical of the court’s 1973 decision. But Casey defied expectations by preserving some protection for abortion.

The devastating setback in Casey prompted some abortion opponents to turn away from politics, prioritizing protests outside abortion clinics or opening antiabortion crisis pregnancy centers. But for many abortion opponents, the quest to reshape the court continued, shoring up the alliance between larger antiabortion groups and the GOP.

So what happens if a post-Kavanaugh Supreme Court undoes Roe?

Some studies indicate that Republicans will have to continue to deliver results that abortion opponents want to maintain their loyalty. While other research challenges this theory, there are reasons to think that the partnership between antiabortion advocates and the Republican Party may be less stable than we think.

First, for the GOP, the post-Roe politics of abortion will be tricky. If states can functionally or formally outlaw abortion, Republican leaders will have to decide how far to go. At first, antiabortion advocates will likely adopt an incremental approach, but make no mistake: The movement expects sympathetic politicians to eventually ban abortion outright.

This position, however, is not popular with Americans more broadly. Polls suggest that if the court overturns Roe, Republican candidates may suffer.

And then Republican lawmakers will have to define what they mean by “abortion” — leaving them even further trapped between the demands of abortion opponents and the preferences of the general public. Antiabortion activists often argue that life begins at fertilization. Would criminal abortion laws encompass the birth control pill or IUD, both of which prevent pregnancy after fertilization? How would an abortion ban affect infertility treatments, which require the creation and sometimes implantation of embryos that are not expected to be brought to term? Republican legislators may try to duck these issues, which seems likely to disillusion abortion opponents.

And overturning Roe might even shatter the synchronicity between the GOP and antiabortion activists when it comes to the Supreme Court. In the 1970s and 1980s, the GOP and abortion opponents didn’t always see eye to eye on the courts. Abortion opponents wanted the high court to identify a constitutional right to life.

But many Republicans resisted, having soured on judicial recognition of new rights after the Warren court enumerated many they disliked. Abortion opponents recalibrated their argument, focusing on the supposed judicial activism of the Supreme Court. Attacking judicial activism appealed to conservatives who disliked other dimensions of Warren court jurisprudence. If Roe is gone, however, abortion opponents may return to pushing a court-recognized right to life, creating tension with some members of the GOP coalition.

Antiabortion activists will also have to ask themselves whether it still makes sense to rely so exclusively on the GOP. Just as the abortion rights movement grew complacent after Roe, abortion opponents may feel that the national battle has largely been won if the court reverses the 1973 decision, freeing them to vote on other issues.

For abortion opponents who don’t like all of the GOP agenda, such as some black evangelical Protestants or Latino Catholics, the reasons to remain single-issue voters may become less compelling, especially if Republican politicians are not willing to criminalize all abortions. This shift seems especially possible given the changes to the GOP in the Trump era.

The Kavanaugh hearings and their aftermath will likely be a big win for abortion opponents and Republicans alike. But it just might shatter their union in the long run.