The Vermont legislature has overridden the governor's veto of a bill to allow same-sex marriage in that state. The most rabid wingers have already begun making a din to adopt a federal constitutional amendment to usurp a state's right in this case. (The 10th Amendment is invoked only selectively by this bunch.) Vermont has had civil unions for nine years without apparent ill effects.
A PS on this subject: Obama's invocationist, Rick Warren, is a liar.