Will the McCain as trigger-happy hothead work? I suggest a different calculus. Is it true? I would suggest that it definitely is, both in personal temperament and policy prescriptions. And I believe that is the better metric, both practically speaking and morally.
Morally, the case is pretty straightforward. McCain really is a hothead. Everyone seems to agree that's true on an interpersonal level. But I don't really care about that. I don't care who he swears at. But over his time in the senate and now as would-be president, he's shown a tendency always to jump to the most confrontational and military-based responses to foreign events, often to almost ridiculous levels. And I think because of that temperament, he's fallen in with and become a useful tool of the DC neoconservatives who view acting crazy and getting people killed as a matter of principle.
I've watched the Bush presidency very closely. I've watched McCain closely for the last decade or so. And I either know or know a decent amount about a lot of the people advising him on foreign policy. And in terms of the physical safety and future of my wife and two sons, let alone the country, I would much prefer four more years of the Bush presidency to a McCain presidency.
The pragmatic reasoning follows from the moral. People speak and argue much more coherently about things they believe in their bones, things that are true. And people with open minds are much more inclined to believe things that are ... well, true, rather than cooked up for maximum polling advantage. In any case, it's very difficult to know what will and won't 'work' in the abstract and in advance. Going with the truth is a more reliable guide.