When California voters quashed the state's court-ordered experiment with same-sex marriage in 2008, gay advocates vowed to fight on. Their latest battleground: a San Francisco courtroom, where a judge will weigh in on the controversial Proposition 8--and hand down the first federal ruling on whether the U.S. Constitution forbids state bans on same-sex marriage.
If California's law is found to violate the 14th Amendment (which guarantees due process and equal protection), it could threaten anti-gay-marriage statutes well beyond the Golden State. Since November, laws supporting same-sex unions have passed in Washington, D.C., but have been defeated in Maine, New Jersey and...