The NRO's Rich Lowry:

I think it’s totally dishonest, and I took away a couple of things from it. One, I think McCain just kind of feels entitled to this cheap shot, because he was genuinely up front about the surge, he was more courageous about it than pretty much any other major politician. So he just feels, though, he can deliver this low blow. And the other thing that is going on, I think, is McCain is much more comfortable attacking harshly and unfairly his enemies within the Republican Party than he is attacking Democrats. And layered on top of this is his obvious, and I think I find it very distasteful, but his obvious hatred for Mitt Romney. If you saw the clip of McCain today, chortling as he was talking about Romney’s flip-flopping, it’s this kind of insincere McCain laughter that masks his true bile that he’s directing towards Mitt Romney. So I find the whole thing, from the dishonesty to the kind of sentiment animosity it’s revealing about Mitt Romney, to be really unworthy of John McCain, and kind of a shame.