Why State Constitutions Differ in their Treatment of Same-Sex Marriage

Some states treat a same-sex marriage as legally equal to a marriage between a man and a woman. Other states prohibit legal recognition of same-sex marriages in their constitutions. In every state that has a constitutional restriction against same-sex marriage, the amendment was passed by a popular vote. The conventional wisdom about allowing voter participation in such decisions is that they yield constitutional outcomes that reflect attitude differences across states. We reexamine the attitude-amendment relationship and find it to be weaker than expected. In particular, we show that states vary in the costs they impose on constituencies that desire constitutional change. Some states impose very low costs (i.e., a simple majority of voters is sufficient for change). Other states impose very high costs (i.e., substantial legislative and voter supermajoriries are requires). We find that variations in the legal status of same-sex marriage across US states is better explained by these variations in costs than they are by differences in public opinion. Our method yields an improved explanation of why states differ in their constitutional treatment of same-sex marriage today. Our findings have distinct implications for people who wish to understand and/or change the future status of same-sex couples in state constitutions.