Party registration is more important than ever when it comes to finding The One.

America’s steady descent into rank partisanship is permeating every aspect of our lives. The latest installment in the saga is “The Home as a Political Fortress” (pdf) published this September in the peer-reviewed Journal of Politics. The paper’s analysis of 50 years of survey data shows that men and women are increasingly picking their spouses based on their politics, and raising families with views to match.

Couples have never disagreed much about politics. What is new is the intensity of partisan animosity and the extremes to which spouses’ attitudes now converge, argues Tobias Konitzer, the chief science officer of PredictWise, which helps progressive groups utilize public-opinion data. In 1965, spouses’ political views were aligned about 74% of the time. By 2016, alignment was up to 82%. Political disagreement among spouses fell from 13% to 5.8% over the same period.

Konitzer and his collaborators studied voter files of 146 million registered US voters (tallying election participation and voter registration) and combined that with survey data over the last 50 years. The researchers also analyzed studies examining the political leanings of hundreds of families in the 1960s and 1970s, as well as conducted original surveys of 559 married couples (and a similar number of parent-children pairs) through a YouGov online panel in 2015.

Before the stark rise in political partisanship (paywall) in the 1980s, couples often came to political agreement as the relationship evolved, says Konitzer. Today, thanks to factors ranging from dating apps to geographic sorting into urban and rural enclaves, ideologically aligned couples can seek each other out, while excluding those at the opposite end of the political spectrum. In 1973, the level of political agreement among relative recent newlyweds was 54%, according to Konitzer. By 2014, it had risen to 74%. This trend held true even in zip codes where political opinions were more diverse, suggesting that politics, not just proximity to like-minded partisans, is behind this sorting.

One reason, the authors speculate, is that partisanship is now a proxy for values in a way it wasn’t when parties were a more even mix of moderates and extremists. Today, declaring oneself a Republican or Democrat is a clear heuristic to answering a range of moral questions about the other person.

Don’t expect this trend to fade away. Parents often pass on their political views to their children. Since frequency and consistency is key to instilling these attitudes, it’s not surprising that the authors found that when parents share ideologies, they impress their views more strongly on their children than parents with divergent political leanings. They also tend to reinforce their own partisanship. For example, in one study, spouses were asked to assess eventual presidential candidates Hillary Clinton and Donald Trump on a 100-point scale in 2015. Participants in relationships where both agreed on their party identification tended to give Clinton and Trump more extreme scores than participants in relationships with divergent political leanings. So, a Republican parent in a Republican-Democratic relationship was likely to rate Clinton higher than a Republican parent in a Republican-Republican relationship.

Trump’s presidency may be pushing the trend into overdrive. Data from dating apps suggest ideology has moved to the center of coupling considerations. After normal election years, the dating app eHarmony reports, the spike in partisan identification in people’s personal profiles fades out over time. The 2016 election was not a normal year. For eHarmony’s 30 million members, the share of men and women advertising their political affiliation tripled in 2017 compared to the prior year.

Men and women, in particular, are becoming politically estranged. In the 1970s, men and women voted for Republicans and Democrats in roughly equal numbers on average. Today, unmarried women are more politically liberal and Democratic, while single men, especially those who are white, skew Republican.

Unsurprisingly, the paper does not end on an upbeat note: “In the aftermath of the most divisive and conflictual election in recent memory, our evidence on family agreement suggests still more discord and animus in elections to come.”