Ahead of the Supreme Court hearings on two gay marriage cases this week, below we use DW-NOMINATE scores to plot the House and Senate votes to pass the Defense of Marriage Act (DOMA) during the 104th Congress (1995-1997). The constitutionality of DOMA will be decided in the second the cases — US v. Windsor — to be heard on Wednesday.
DOMA passed both chambers of Congress overwhelmingly in 1996: the House by a 342-67 votes and the Senate by a 85-14 vote. The spatial (geometric) model of choice performs well in picking up the internal divide in the Democratic Party based on both dimensions (ideology and region) over gay rights. The 66 House Democrats and 14 Senate Democrats who opposed DOMA are concentrated in the liberal, non-Southern wing of their party. Note that the cutting lines in the House and the Senate are nearly identical, indicating that the ideological split was consistent in both chambers.
We, like many other observers, are struck by how quickly public opinion has shifted on the issue of gay marriage and, from a spatial perspective, the mapping of this issue has changed in congressional voting. While these sorts of votes divided Democrats ideologically until only recently, the cutting line appears to have shifted rightward and will likely differentiate Republicans (both in and out of Congress) on the basis of ideology in the future. We also plot Senator Rob Portman’s (R-OH) DW-NOMINATE score (since they are comparable within chamber over time) given his recent switch in support of gay marriage.