Matt Yglesias makes a great point:
As John McCain likes to say, he has at various points in time disagreed with George W. Bush's tactical approach to Iraq. But in the ways that matter, he's generally agreed with Bush's strategic vision. ...
In some ways, I think McCain himself doesn't quite realize how Bush-esque he is. He clearly doesn't like Bush, and has been disliking him for a long time. But that kind of personalized, overblown disdain for Bush-the-man can wind up leading you to overestimate Bush-the-grand-strategist. To McCain, Bush's policies have failed because of Bush. Replace Bush with McCain and shift tactics around the margins, and the same basic ideas should work out fine. It's a nice theory, but I don't think it's a true theory.
Exactly right. McCain believes the issue in Iraq was competence--he doesn't think Bush had it, and is confident he does. But, as many argued at the time of the invasion, the bigger problem was that it's just really, really hard to occupy a large country, particularly a large Muslim country rife with sectarian divisions, and you should try to avoid it if at all possible. Bush didn't try to avoid it, and McCain wouldn't have either. Worse, like Bush, he still doesn't think we should have tried to avoid it, even with the benefit of hindsight.