Last Thursday, the day after President Obama finally endorsed gay marriage, his campaign released a video that faults his presumptive Republican opponent, Mitt Romney, for not doing likewise. "President Obama is moving us forward," the ad says. "Mitt Romney would take us back." In a sense, says Senior Editor Jacob Sullum, Obama is the one going back, returning to a position he took as a political novice in 1996. But the same changes in public opinion that made it thinkable for him to stop equivocating on gay marriage present a challenge to Romney as he repositions himself for the general election.