The political price for supporting same-sex marriage can be hard to predict. Four years ago, Assemblywoman Teresa R. Sayward, a Republican and a Catholic from a conservative district in the Adirondacks, voted in favor of same-sex marriage after making an impassioned speech about her son's struggle with his gay identity.

"The night I took the vote the first time, I was told by my Republican colleagues that I would never get elected again," she said. Since then, Ms. Sayward has been re-elected twice.