Part of the McCain-Obama contest is about "temperament," beyond the particular issues, and its no wonder the most fervent supporters of each can't stand the other. As the VP selection process indicates, they operate in very different ways.
John McCain remains in many ways the fighter-jock. He trusts his instincts. He's willing--he enjoys--flying off into new directions. A successful fighter pilot is not stupid, by any means, but there's not a lot of time in a dogfight for deliberation. It's best to move, and move now, before the opposition is sure where you are. If your choice is not the ideal move, that may still be ok. If you can keep shifting faster that the other guy, you can correct your errors while his errors accumulate. It's Boyd's OODA: Observe/Orient/Decide/Act (repeat as necessary).
Barack Obama is by training and temperament a jurist. For him, the decision-making model is the analytic loop drilled into first year law students--IRAC: Issue/Rule/Analysis/Conclusion. It's essentially conservative, in the sense that it discourages rapid change or experimentation. Oddly enough, for the "change" candidate, there's remarkably little in his program that hasn't been knocked around in Democratic think tanks for years.
Fighter jocks think tactically, but they can miss the big picture. They focus on how to improve the situation in Iraq, but are less likely to ask whether the war is necessary. Jurists think in terms of general principles and precedents, but avoid the particulars. Once they decide Iraq is the wrong war to fight, it doesn't much matter to them what is happening on the ground.
Jurists campaign systematically. They organize, they build their forces, they organize some more. They stay on message. They think things through. They strive to avoid mistakes. They conduct long search processes that result in conventional choices. Fighter jocks enjoy coming from a direction you didn't expect. They take long gambles. They go with their gut. They hold the decision close, make it quickly, and look for ways to rattle the opponent. On occasion, they crash. Then, if it doesn't kill them (and on occasion those who fly with them), they learn to do better.
(Remember the movie Top Gun? The hero's call sign was "maverick.")
Long political campaigns favor the systematic, the organizer, the jurist. The last two months before the American election, down and dirty, with charge and countercharge, play to the strengths of the fighter jock.