Philip Klein has a nice chart out reminding us that in most cycles the veepstakes run right up until the last few days before the party’s national convention. As he points out, “The bottom line is that Romney would be better off waiting as long as possible to make his choice so he has the most information he can when making his final decision.”
That’s right. Klein mentions the possibility that the campaign narrative might shift so that a different candidate would seem logical (if, in the example he gives, a major foreign crisis makes selecting a running mate with relevant experience seem like a better idea). But I don’t think that’s really the issue here; after all, even with the conventions these days pushed back much farther than they used to be, there’s no real way of knowing if the issues that seem pressing in late August — but not now — would also seem pressing in late October. And at any rate, there’s very little evidence that picking a “narrative” candidate as running mate can do anything for the ticket, anyway. Remember, the upside of a good VP pick is probably a couple of percentage points in the running mate’s home state.
No, Klein is correct that the reason to wait is to wait for new information, but the relevant information here is from vetting. First of all, Mitt Romney wants to be sure that noisy and influential factions within the Republican Party will accept his pick. And, second, he wants to give the national press some time to poke around at the candidates, helped no doubt by the other party’s opposition research team and any enemies the potential running mate may have, which is why it makes perfect sense for the campaign to leak out any names under consideration. Team Romney wants any bad news on Veepstakes contestants to surface now, not after the selection.
The bottom line: The correct strategy for picking a running mate is to do no harm, either in the campaign (Palin, Eagleton) or later (Agnew). There’s no particular reason to rush; you’re going to get the (presumably positive) immediate story some time between, in this case, May and August, and after that it will go away and that’s about the end of it. Might as well get that closer to the election, no? And beyond that, it’s difficult to think of any real upside from picking early, which is perhaps why it’s rare to do it. So if Romney is as good of a technocrat as we're supposed to believe, don't expect a pick for another month or more.