MANCHESTER, N.H. — Expected Republican presidential contender Mitt Romney tread on socially dangerous ground last night as he talked about the need to "hang" a misery index around the neck of Barack Obama, the nation's first black president. Romney almost immediately caught himself, with the English major declaring "metaphorically" speaking, but the mix of nervous laughter with applause indicated at least some in the audience realized its potency. Romney said: "You remember during the Ronald Reagan/Jimmy Carter debates? That Ronald Reagan came up with this great thing about the 'misery index,' and that he hung that around Jimmy Carter's neck,...