McCain doesn't understand his own policies. Hilzoy said it perfectly:
That's a scary thought.
There's a pattern to this. McCain seems to have a few ideas about economics. Spending is out of control, and if we just restrain it, things will be OK. (Moreover, none of the spending he proposes -- e.g., the spending required to add 200,000 troops to the armed forces -- actually counts.) People should have the right to put their own tax money into their own Social Security accounts. Cutting taxes raises revenue. And that seems to be about it.
Since he doesn't actually understand what he's talking about, he periodically says something ill-advised -- that he supports privatizing Social Security, that he'll balance the budget in four years, and so forth. Then his advisors walk him back -- as they have already done with his promise to balance the budget by the end of his first term, and as I expect they'll do shortly on Social Security.
But it's not just on economics that this happens. Recall his advisors taking back his promise to kick Russia out of the G-8, the way he has needed to be corrected about whether Iran is training al Qaeda, or whether al Qaeda is Shi'a, or how many troops we have in Iraq, and so forth. And remember that he doesn't seem to know what a cap and trade system is, despite having co-sponsored cap and trade legislation in Congress, and having a cap and trade system as a central part of his energy policy.
He has a few ideas lodged in his head, without anything like the background he'd need in order to question or assess them, and without any discernible interest in learning more. He doesn't keep basic, basic facts straight, or know really elementary aspects of his own policies.
I never thought I'd end up covering John McCain like this. I expected, after eight years of Bush, to be able to argue about genuine philosophical and policy differences, rather than going on about the most basic matters of competence. But McCain's performance so far is just frightening. We've had eight years of a clueless President who governs on the basis of his gut plus a few stray ideas that wafted in on the breeze and somehow stuck. We do not need four more.