Consider this: of the five presidents who won election in the years before Watergate, four had served as United States senators. (The fifth was Gen. Dwight D. Eisenhower, who could hardly have been considered a novice in the ways of Washington.) Since that time, however, four of the six presidents elected had been governors who never served in Washington and who made systemic reform their central campaign themes.

In recent campaigns, the outsider ethos has become so powerful that, for a certain kind of candidate, lack of experience in Washington — or in politics altogether — translates into a defining virtue. Thus could Sarah Palin rise to iconic status in her party on the strength of her résumé as a small-town mayor and brand new governor — and then quit the governorship altogether, on the novel theory that she was actually doing a disservice to the public simply by holding elective office and collecting a salary for it.

There’s a tension, often irreconcilable, between our romantic vision of the outsider candidate, on one hand, and our basic threshold for credibility in those who govern, on the other. Sure, we want colorful, outspoken characters who aren’t part of a corrupt political system. We just want them to be tested, scandal-free and ready to govern at the same time. Is that so much to ask?