The basic way to understand McCain is that neoconservative foreign policy is his ideological core. Everything else about his ideology can shift radically depending on his ambitions, circumstances, and whom he’s most angry with at any given moment. He favored immigration reform under George W. Bush, abandoned it to refashion himself as a “build the dang fence” border hawk, and, in the wake of last November, embraced it again...Perhaps. I personally subscribe to the other theory: it's a combination of electoral incentives and personal vendettas.
But the foreign policy hawkishness has remained constant.
What we need is for a neocon to pick a fight with McCain (to see if he'll go dovish as a reaction) or for some electoral situation in which hawks are at a disadvantage. I don't think either of those has ever happened in his career, or at least I don't think he's perceived belligerence in foreign affairs to be an electoral negative.
What both theories have in common is the idea that McCain is largely indifferent about policy at least of outside of national security and foreign affairs. Well, indifferent isn't quite right...McCain can be quite passionate about all sorts of issues while he's engaged in them; it just doesn't seem to be based on any kind of consistent ideology, or even a consistent view on the specific issue.
I am wondering how McCain's push for reconciliation with Vietnam counts here. I'd argue that it cuts against Chait's theory and in favor for everything being either electoral or, in this case, personal. I'd also argue that his relatively moderate position on the Chuck Hagel nomination fits my theory better; McCain opposed the first cloture vote and final confirmation, but he provided the key vote for cloture in the second cloture vote. Perhaps because he was more annoyed with Ted Cruz than he was loyal to the neocons. But neither of these is anywhere near conclusive.
Anyone else have examples that can help resolve this one?