In the days immediately before and after passage of the landmark health care reform bill, Mitt Romney responded so forcefully as to suggest his own political fate is tied to the new law. It may well be. Just as health care, or “Obamacare,” as it is derided on the right, hangs over this year’s midterm elections, it is already casting a shadow on the 2012 presidential contest — and its GOP front-runner. What was once thought to be an asset for Romney, his passage as Massachusetts governor of a health care mandate for the state’s residents, now poses a potentially...