In a sense, "gaffe" is overly forgiving. It implies that McCain means to say the right thing, but tends to misspeak. I don’t see it that way at all. "Gaffe" suggests McCain knows what he’s talking about, but is burdened by the occasional embarrassing verbal faux pas.
But that’s not the real story here. The important point is that McCain, most, seems hopelessly clueless and confused. That’s far more significant than the occasional "gaffe."