Same-sex marriage opponents counted black voters among their allies leading up to November’s election, expecting them to help overturn legislation allowing same-sex couples to marry in Maryland. Polls in the months before November’s referendum on same-sex marriage seemed to back them up, with black residents showing less support than whites. But as the months wore on, opposition softened, especially in the face of endorsements from President Obama and prominent entertainers, as well as a media campaign that included clergy, athletes and other public figures. By Election Day, voters in the state’s large, predominantly black jurisdictions — Baltimore and Prince George’s...