Scott Brown's victory in Massachusetts has most Republicans hopeful about midterm elections. It has Mitt Romney hopeful about 2012. In many ways, the former Bay State governor never ended his 2008 presidential campaign. From a perch atop his Free and Strong America PAC, Mr. Romney has been raising money, nurturing his team, keeping himself in the national spotlight. With the Massachusetts Senate race, he sensed an unexpected opportunity to step to the front of the GOP presidential ranks. He played it nicely. Aware that many voters have mixed views of his governorship, Mr. Romney stayed in the shadows, leaving other...