McCain-Romney = "do no harm"? Not in the part of the universe I'm aware of.
Just to clarify, I think that picking Romney would be a mistake, and that the GOP ticket would be weaker for his presence on it - for some (though not all) of the reasons David Frum's friend lays out here, and for others as well. But Romney doesn't come with anything like the risks and/or unknowns associated with some of the other names that have been floated as potential veeps - names like Joe Lieberman, like Tom Ridge, like Bobby Jindal, like Meg Whitman. True, picking a Mormon might depress evangelical turnout, but a McCain-Romney ticket wouldn't risk a serious intra-party civil war the way McCain-Lieberman or McCain-Ridge might. True, Romney is an epic flip-flopper, but he isn't an ideological black box with no governmental experience like Whitman. True, he's got a phoniness problem, but he isn't twelve years old like Bobby Jindal. True, he has some rich-guy liabilities ... but he has a real record of achievement both in and out of government, he isn't a D.C. insider, he won't get embarrassed by Biden in a debate the way, say, a Sarah Palin might, and his strengths dovetail reasonably well with McCain's message, as Yuval Levin argues. Again, I'm no Romney fan and I think McCain can do better (though I'm damned if I know who he should pick - or who he has picked, I guess I should say at this point). But Mitt, for all his slew of weaknesses, is much more of a known and tested quantity than most of his apparent competition for the slot, and I think that's enough to make him one of lower-risk options available, even if he's considerably lower-reward as well.