DES MOINES, Iowa -- Romney sharpened the sell for his health care plan here at Des Moines University. For the first time, he gave a time frame on its follow-through, and he provided a bit more context about his own background on the issue before touring the Skiff Medical Center in Newton. “I just want to underscore something,” he said, concluding his address at the university, “we can get everybody in this country insured…. My estimate that from the time you would put in place this program, pass the legislation necessary to put in place this program, within four years...