I'm no logician. And I certainly don't want to pick a fight with Clinton who was one one of the smartest presidents the U.S. has ever produced. But I don't think the plumber-chef thing works as an analogy.
Sticking with Clinton's medical example, what Obama is saying is that you had some experienced doctors who unwisely committed a heinous case of medical malpractice, i.e., the Iraq invasion.
So what you want is a doctor who may have less of the "experience" of the malpracticing physicians but better judgment.
Obama, just as much a politician and lawmaker like those he criticizes, is certainly not saying that the voter-patients should turn to someone completely outside the field for a better result, the plumber or chef of Clinton's example.
http://weblogs.baltimoresun.com/news/politics/blog/2007/12/by_frank_james_when_former.htmlthat was ridiculously lame; more so since it came from one of our smartest presidents ever.