First, 30 percent of married households contain a mismatched partisan pair. A third of those are Democrats married to Republicans. The others are partisans married to independents. Perhaps unsurprisingly, there are twice as many Democratic-Republican pairs in which the male partner, rather than the female partner, is the Republican.

Second, 55 percent of married couples are Democratic-only or Republican-only, which raises a question: Is that a big number or a small number? In other words, is there more or less partisan intermarriage than we should expect? Here are two ways we try to answer that. We can compare interparty marriages to interracial marriages. Using voter registration data, we can do this in three states, Florida, Louisiana and North Carolina, where public voter files list everyone by their party affiliation and their racial identity. In those states, 11 percent of married couples are in Democratic-Republican households. In comparison, only 6 percent of married couples are in any kind of interracial household. At least in these states, there’s about twice as much interparty marriage as interracial marriage.