Okay, while others are digesting the Biden pick, let's skip ahead to the next question: how does John McCain respond? While Biden is a solid pick for Obama, he is not a game changer. Though Biden is a white Catholic with some family roots in Pennsylvania, he doesn't bring any state directly into play. He may or may not help Obama assuage the anger of the Hillary holdouts.

Taking all of this into account, what will McCain do? The names on his short list, from what we know right now, are Pawlenty, Romney, and Lieberman - not necessarily in that order. Ridge was ruled out by an anonymous RNC official last week - which doesn't necessarily mean he's off the list - and after the push back from conservatives over the possibility of a pro-choicer on the ticket, I would suspect Lieberman's chances are slim to none.

Given that McCain is so close in the polls - well ahead of where his campaign probably thought they'd be at this point in the race - there really isn't any need for a a Hail Mary, "game changer" type pick - especially a pro-choice candidate who would alienate the conservative base. That's even more true now that Obama went with a "safe" choice as opposed to picking a game changer of his own - like Hillary.

So McCain should pick a pro-life running mate, probably from a key battleground state. Economic experience and/or youth would be preferable, but not absolutely necessary. That leaves Romney and Pawlenty in the mix, probably in that order. A story last week about a possible McCain rally in Ohio on August 29 brought Rob Portman's name to the forefront of the discussion. But the person who might make the best pick of all for McCain is John Kasich.

With the recent downward trend for Obama in national and state polls, along with the news yesterday that Obama is suspending television ads in 7 "red" battleground states, it looks increasingly less likely that Obama is going to fundamentally "change the map" this year. Instead, 2008 is shaping up as a repeat of '00 and '04, with the same handful of key battleground states making the difference.

On one level, Obama's choice seems to validate this idea, because Biden is clearly not a "change the map" type of pick. If anything he may be the opposite: an admission that this election will be a hard fought scrap over the same traditional turf.

On the other hand, Obama clearly chose someone he thought would help boost him in a generic national sense, because if you look at the states where this election is likely to be decided (Ohio, Michigan, Florida, Pennsylvania, Colorado, Iowa, New Mexico, Nevada, Virginia) it's not clear that Biden will offer much material help in any of them.

Now it's McCain's turn. He wisely kept the advantage of making his pick after Obama, and we'll see whether he uses his choice in a more tactical way to try and improve his position in a battleground state. Guys like Romney or Kasich might only help marginally in Michigan and Ohio. But again, the way this race is trending, a little bit of help in those states might turn out to be decisive in the end.