STRATHAM, N.H. – Mitt Romney's political backyard is the most promising terrain in his second bid for the Republican presidential nomination. It's also the most perilous. The former governor from neighboring Massachusetts has a vacation place in New Hampshire, so the state really is his second home. He's well known and well established here, and he's putting more emphasis on the Granite State, which holds the nation's first primary, than he did four years ago. He'll be in Manchester for a seven-candidate debate Monday night. But the state's proximity to Massachusetts is a two-edged sword. Voters know a lot about...