Welcome to Secret Identity, our regular column on identity and its role in politics and policy.

The debate over Brett Kavanaugh, President Trump’s nominee to replace Anthony Kennedy on the Supreme Court, is likely to be dominated by discussion about abortion as the court, if Kavanaugh is confirmed, would have five solidly conservative justices, which may mean it’s willing to strike down Roe v. Wade. And that discussion will likely be split by party: Almost all the Democrats you see on cable news and on the floor of the Senate will strongly defend abortion rights, while anti-abortion activists will be among Kavanaugh’s most prominent advocates, even if they don’t outright say they think he will vote to strike down Roe.

But the way the abortion debate plays out in national politics, particularly around judicial nominations, does not reflect how the broader public views this issue. The issue is not a 50/50 Democrat/Republican split, as the plurality of Americans consistently take the “pro-choice” position over the “pro-life” one. And the public, unlike political elites, is not completely divided along party lines on this issue. There is a large bloc of Republicans who support abortion rights. There is a smaller, but still sizable, group of Democrats who oppose abortion rights.

A third of Republicans are pro-choice Share of poll respondents by views on abortion, June 2017 Party Identification Legal in all/most cases Illegal in all/most cases Republican 34% 65% Independent 60 38 Democrat 75 22 Source: Pew Research center

Yet we aren’t likely to hear those voices. Why not? Because they have been disempowered in each party. The politics of abortion are in some ways a story about party coalitions, and each party has a bloc that dominates how its party handles the issue (conservative Christians in the GOP, women’s rights activists among Democrats). Because of the power those blocs have, being anti-abortion rights has become a part of the identity of the Republican Party, even if its voters don’t all share that stance; similarly, the Democratic Party is the pro-abortion-rights party.

Let’s take a detailed look at how this dynamic plays out in each party.

Republicans

I don’t want to avoid the obvious — there is a partisan split on abortion. Pew Research Center polling conducted in 2017 found that about 75 percent of Democrats say abortion should be legal in all or most cases, compared to 34 percent of Republicans. But 34 percent ain’t nothing. And polls consistently find that about a third of Republicans say that abortion should be legal or agree with the Roe v. Wade decision.

Who are these people? Self-identified moderate and liberal Republicans, in many cases; a majority of this group thinks abortion should be legal in most cases, according to Pew.

But this bloc has virtually no power in the GOP. Of the 236 Republican members of the House of Representatives who voted on the bill, just two opposed a provision last year to ban abortions after 20 weeks. Both are now retiring, leading Politico to declare recently that the pro-choice wing of the party is basically dead in the House.

Daniel K. Williams, a historian at the University of West Georgia and author of the books “God’s Own Party: The Making of the Christian Right” and “Defenders of the Unborn: The Pro-Life Movement before Roe v. Wade,” argues two key factors help explain the shrinking ranks of the pro-abortion-rights bloc of the GOP on Capitol Hill. First, the party is increasingly weak at the congressional level in the Northeast, where some pro-abortion-rights Republicans had been able to win in the 1980s and 1990s. Second, the rise of the Christian right in the GOP and its emphasis on limiting abortion means that Christian conservative activists make sure anti-abortion candidates are elected in primaries and general elections, particularly to Senate seats, where they can then vote to confirm anti-abortion-rights judges.

It’s not just that the pro-abortion-rights bloc of the GOP can’t seem to gain much ground in electing members of Congress who share its views — this bloc doesn’t have much influence at the grassroots level either. Last month, Susan Bevan and Susan Cullman, leaders of a group called Republican Majority for Choice, announced that they would leave the GOP and that their group would cease operations, arguing there was no room for their cause in the current Republican Party, in part because there is a “hostility to women within the Republican culture.”

Another way to think about the dynamic that Bevan and Cullman are describing is that Republicans tend to be resistant to ideas linked to “identity politics” centered around gender (or race) but embrace those based on Christian faith. Anti-abortion Republicans tend to ground their arguments in part on religion.

“Ever since Reagan, they’ve been able to collapse pro-life with being a Christian,” said Marcia Chatelain, a historian at Georgetown University and an expert in social movements, referring to anti-abortion activists in the GOP.

But given that the plurality of Americans support abortion rights, Republicans with more liberal views on abortion aren’t alone. If the GOP moved to the left on this issue, it might help the party electorally. But in reality, softening the party’s position on abortion would be a huge risk, potentially weakening the GOP’s very fruitful alliance with white evangelicals, who exit polls suggest were more than 40 percent of the voters who backed Trump in 2016. We don’t know if abortion is the issue that keeps white evangelicals in the GOP camp, since they are conservative on other issues too. But I’m guessing Republican leaders would rather not experiment and test this proposition.

Add all that up, and here’s what you see: If the Republicans in the Senate reflected the views of the broader party, about 17 of them would be pushing to make sure Kavanaugh wouldn’t vote to strike down Roe. But in reality, Maine’s Susan Collins and Alaska’s Lisa Murkowski are the only Republicans who regularly oppose anti-abortion legislation in the Senate. Being two out of 51 Senate Republicans makes them a very small minority, and they will be under heavy pressure not to block Kavanaugh’s confirmation.

Democrats

There are fewer anti-abortion Democrats than there are pro-abortion-rights Republicans. About a fifth of Democrats say abortion should be illegal in most or all cases, according to Pew. Similarly, a Kaiser Family Foundation poll recently found that about 16 percent of Democrats would like to see Roe v. Wade overturned. Who are these Democrats? Many are people who describe themselves as moderate or conservative Democrats, or black Protestants.

But as with being pro-abortion-rights in the GOP, it’s hard to get elected to Congress as an anti-abortion-rights Democrat. Just three House Democrats and three Senate Democrats (Bob Casey of Pennsylvania, Joe Donnelly of Indiana and Joe Manchin of West Virginia) backed the bill banning abortions after 20 weeks.

What’s going on? It’s an inversion of the GOP’s narrative. There was once a larger bloc of anti-abortion-rights Democrats in Congress, but many of those members were from the South, and those seats are now largely occupied by Republicans as the Democrats’ strength has declined in that region. Also, as the Christian right made it a key GOP policy goal to reverse Roe v. Wade and limit abortions, pro-abortion-rights groups pushed the Democratic Party to make defending abortion rights more central to the party’s identity — so much so that the party inserted a provision into its 2016 platform that called for the government to overturn a ban on using federal funding to pay for abortions. The ban, called the Hyde Amendment, has been in place since the 1970s.

This leftward shift among Democrats has occurred as groups that promote women’s rights have gained more power in the party. While Republicans’ “identity politics” are based more on faith than gender, for Democrats it’s the other way around.

The number of Democratic women in Congress has surged in the last two decades, and now about a third of Democrats in Congress are female. Many of those women got support from the group Emily’s List, which supports female Democratic candidates, but only those who back abortion rights. Planned Parenthood, which provides reproductive health services, including abortions, is deeply enmeshed in Democratic politics. Its political action committee invests heavily to help the party win elections.

“The essential issue with abortion [among Democrats] is that it’s not about access to a perfectly legal health choice,” Chatelain said. “It’s about all of the issues around state rights, around privacy, about gender and the family, about wages, I think abortion has become a proxy for a number of very complicated issues. … It’s about so much more on the left.”

So, like the pro-abortion-rights Republicans, the anti-abortion Democrats are basically powerless in and out of Congress. But they are getting a slight acknowledgement in the Democratic campaign to defeat Kavanaugh’s nomination. The organizers of the anti-Kavanaugh campaign are urging senators to oppose the nomination, on the grounds that he might vote to strike down Roe and that he might vote to get rid of the Obamacare provision that bars insurers from denying people coverage if they have pre-existing conditions. A senator like Manchin may want to define his opposition to Kavanaugh more in terms of health policy than abortion.

But no matter Manchin’s rationale, Democratic activists will be furious if the senator votes to confirm Kavanaugh at a time when Roe may hang in the balance — and Republicans similarly will be very angry with Collins if she opposes Trump’s Supreme Court pick.

“Senator Collins might call herself pro-choice, but if she has a 100 percent voting record for the judicial nominees that the pro-life movement is counting on to overturn Roe v. Wade, the pro-life movement is not going to mobilize against her, and the Republican Party will be happy to have her remain in the Senate,” said Williams. “Senator Casey might call himself pro-life, but if he votes with his party when it comes to judicial nominees, the pro-life movement is not going to support him, while the Democratic Party will be happy to have him in its ranks,” he added.

What else you should read

The New York Times editorial board declares, “Make Way for Young Democratic Leaders,” and criticizes the party’s current leadership for blocking younger members’ path to power. It’s worth reading. But it’s a little, well, ageist in my view. Isn’t the strongest case against Nancy Pelosi and other longtime House Democratic leaders that the party has lost four straight House elections under their command, not that they are almost 80 years old?

This letter from influential liberal activists, including a number of prominent black women, urges Pelosi and Senate Democratic Leader Chuck Schumer to aggressively defend Rep. Maxine Waters from attacks by Trump and other Republicans. It is part of a broader narrative in the Democratic Party: Black women, who overwhelmingly back Democratic candidates, are trying to have more influence on the party’s internal operations.

If you have ideas for this column, you can reach me via email (perry.bacon@fivethirtyeight.com) or on Twitter (@perrybaconjr).