Mitt Romney offered an enthusiastic defense last night of the comprehensive health care law he helped create four years ago in Massachusetts, even as he pointed to crucial distinctions between it and a similar national program enacted last week by Democrats. “Overall, ours is a model that works,’’ Romney said in response to a question after a speech at Iowa State University. “We solved our problem at the state level. Like it or not, it was a state solution. Why is it that President Obama is stepping in and saying ‘one size fits all’ ’’? Obama’s signing of a federal...