With his narrow loss in Tuesday’s Illinois primaries, eight-term Chicago-area congressman Dan Lipinski, one of the last pro-life Democrats on Capitol Hill, became the most recent casualty of the partisan divide on abortion in the United States. His victorious challenger, Marie Newman, a business consultant and nonprofit founder who has never held office, had support from a number of progressive groups, including pro-choice organizations like Planned Parenthood, EMILY’s List, and NARAL Pro-Choice America.

Lipinski’s position as a pro-life Democrat was once fairly common in Congress, but it has made him an outlier on today’s Capitol Hill. A Catholic (like his equally pro-life father, William, who held the seat before him from 1982 to 2004), Lipinski often invoked his faith as a reason for his pro-life positions. Yet Newman is also Catholic, a detail she has emphasized during her campaign even as she has been steadily committed to pro-choice policies.

Incumbents free from scandal seldom lose primaries. Lipinski’s loss, following his narrow win against Newman in 2018, suggest his problem was being out of touch with Democrats in his district, which stretches from Chicago’s southwest side to southern and western suburban areas. He voted against the Affordable Care Act in 2010 and refused to endorse his fellow Chicagoan, Barack Obama, for re-election in 2012. The district has also changed since the elder Lipinski was elected, stretching ever deeper into the suburbs and witnessing the slow decline of the vestiges of the once mighty Cook County machine to which the Lipinskis belonged.

Lipinski’s unwavering abortion position (and his relative conservatism on other issues) also contrasts with that of another Catholic Democrat, Joe Biden, who did a 180 on abortion over the course of his long career. Biden went from supporting a pro-life constitutional amendment in the 1980s to rejecting the Hyde Amendment banning federal funding for abortions at the beginning of this campaign and even the limits on late-term abortion that he backed in the 2000s.

“ Lipinski’s unwavering abortion position also contrasts with that of another Catholic Democrat, Joe Biden. ”

Biden’s remarkable political longevity, and the imperative to be broadly acceptable in the party whose presidential nomination he has sought for decades, have required many such evolutions. Had the former vice president not moved in this direction, unlike the unchanging Lipinski, Biden might not be the next Democratic nominee for president. Indeed, he might not even have held his Delaware Senate seat. Instead Biden easily carried Lipinski’s district against Bernie Sanders—whose pro-choice record is far lengthier—in the same primary that Lipinski lost it.

Biden’s reversal on abortion is far from uncommon. Donald Trump was once publicly pro-choice, as were Mitt Romney and both Presidents Bush earlier in their careers. Nor is Biden’s evolution limited to this issue. After being unsupportive of LGBT rights for much of his career, Biden belatedly cosponsored the Employment Non-Discrimination law in 2001, well after a majority of Democratic senators had signed on to the bill, and famously came out for same-sex marraige ahead of President Obama in 2012. He also recently turned against the death penalty he long supported.

In a recently published academic article, we show that legislative divisions on abortion have become less denominational and more partisan over several decades. In 1967, six years before Roe v. Wade, the California state legislature voted to liberalize the state’s abortion laws, which had previously barred abortions except to save the mother’s life. At the time, legislators’ religious affiliation, not their party, was an important predictor of their votes. Catholics were mostly against and Protestants and Jews were mostly for. The issue wasn't very partisan.

“ Incredible as it seems today, Republican voters were slightly more pro-choice than Democrats until the mid-1980s. ”

Most Catholics were Democrats, and most Catholics were pro-life (although the term wasn't yet used). Many Republicans supported the new law, including Governor Ronald Reagan, who later said he had made a mistake in doing so. This was true not just of elected officials on Pennsylvania Avenue and in statehouses, but voters as well. Incredible as it seems today, Republican voters were slightly more pro-choice than Democrats until the mid-1980s.

This gradually changed as both parties incorporated new interest groups that cared about the issue: feminists for Democrats and the religious right for the GOP. This new alignment altered the incentives of elected officials whose individual moves to appease these new constituencies helped define the parties’ images and draw in more of them, which in turn increased the incentive to please them by taking on new positions. Reagan’s closeness with the Christian right was a key development in sharpening the party divide on abortion.

We show that a significant part of the shift of the issue from the denominational divide to a partisan one—in which California was ahead of the rest of the country—was adaptation or flip-flopping by incumbents, much as Biden has done. In other cases, legislators retired or were defeated and replaced by someone with a position more in line with their party's current commitments. This was a very gradual process that has been underway for over 40 years that is nearing completion, and it is highlighted in the contrasting fates of Biden and Lipinski in the same district on the same day.

It’s easy to be cynical about the politicians’ adaptation and to see it all as opportunism. Lipinski’s refusal to bend on a matter of conviction, when he knew it might cost him his seat, may strike many as admirable, even if they don’t share his view on abortion. But not all changes of position are simple careerism; people really do grow and learn. Many ordinary people as well as politicians have changed their minds on LGBT rights issues in the past two decades, for example. We cannot always say where conviction ends and calculation begins.

The results of some seemingly opportunistic shifts may also seem positive in retrospect. There is a good case, for example, that LBJ’s move from Southern segregationist to champion of civil rights was driven by presidential ambitions, which required him to take positions acceptable to Northern Democrats. The combination of career politicians, who are inevitable, and representative government, which is desirable, makes such changes necessary, regardless of the motivation behind them. A representative government needs its Bidens as well as its Lipinskis. Maybe even more.

David Karol is Associate Professor of Government & Politics at the University of Maryland.

Chloe Nicol Thurston is an assistant professor of Political Science and Faculty Fellow at the Institute for Policy Research at Northwestern University.