When Marcia Hams and Susan Shepherd cut into their wedding cake at city hall in Cambridge, Mass., on May 17, 2004, after becoming the first same-sex couple in the U.S. to complete a state-sanctioned marriage application, they probably hoped their union would open the floodgates for gay couples across the country. But instead, it became a high-water mark for same-sex marriage as the acrimonious debate over the issue raged on--a moment equaled only by a California Supreme Court's ruling in mid-May overturning the state's ban on gay marriage.
Same-sex marriage has a short but heated history in the U.S. It first...