"Your argument, then, is that the winning strategy for political office is to play up one's unsuitability for public office. I'm not going to dismiss that out of hand, but it's not a statement that should be accepted at face value. Do you have examples of other protest candidates that have used this strategy effectively?"
Not really - the point I'm making is that the winning strategy is often disruption in general. Donald Trump is a bizarre case, and I think a lot of the reason that he's gotten as far as he has is that the political establishment in the United States is far more despised than it is in, say, Canada. So, in this case, a message to the effect of "I may be a jerk, but I'm not one of THOSE jerks" is enough. In Canada, that wouldn't fly - as I mention in the analysis, if Trump had admitted that he hadn't paid his taxes in 15 years in a Canadian debate, his opponents would have nailed him and his campaign would be effectively done as of that moment.
That said, we've seen a number of successful disruption strategies in Canadian elections over the last few years. To use a very clear example, Dalton McGuinty won the provincial election in Ontario by disrupting the Conservative strategy - while they were very negative, he ran a very positive campaign that left the Ernie Eves Conservatives scrambling to adapt to (and they didn't, and have been out in the political wasteland ever since). The trick is that what you are attempting to disrupt has to be something that has had sufficient time to become established. So, if Trump was attempting a strategy like this at the end of the Bill Clinton years, Congress and their obstructionism would not have become so established and detested that it would have worked.
What makes this situation very dangerous is that by presenting himself as a viable outsider candidate (a threshold he reached as soon as he got the Republican nomination), he IS expanding his voter base to include a number of people who would otherwise not vote because they've lost complete faith in the system. The mistake that I think a lot of commentators are making is to think that the people supporting him don't realize he's a blowhard and a liar - a lot of them DO, but still consider him better than the blowhards and liars that are in office already. So, his attack on the political establishment DOES make this election winnable for him, and if he does win, the United States gets a President whose is very unpredictable and quite possibly dangerous.