Now that BHO has chosen Joe Biden as his running mate -- and it is a very good choice that he has made, it is time to enjoy the guessing game about whom Big Mac will pick. Perhaps the most effective way to enter this game is to start by tagging who he will NOT pick. So here goes:

1.He will NOT pick a woman candidate, at least not one with political potential. Why ? Simple. He won't do so because to do so would be to create a rival to Hillary Clinton. John McCain needs Hillary to be at least neutral in this race (and neutral she will be, no matter what she says) or at least needs her crucial supporters to be neutral, or even IN His camp. If he raises up a rival to Hillary in, say, Condi Rice, or even Meg Whitman, that implicit, unspoken alliance is put at big risk.

This factor is also one reason why BHO did not choose Kathleen Sebelius.

2.Big Mac will NOT pick a VP whose chief appeal is to right-roots. John McCain needs to show that can GOVERN. The campaign cannot be about the campaign itself: and it is only in the campaign that right-roots -- the "social conservatives" -- make their noise. Once the campaign is over, then governance begins. Thus John McCain will choose someone whom he thinks can help him GOVERN. This means someone who understands Washington and understands the budgeting process chiefly. Because John McCain thinks that the major correctives that need to be made to the Federal Budget are, first, reforming the Defense Appropriation game and, secnd, ending earmarks and other irrational spending choices, he will likely NOT choose a VP whose understanding of Washington is in the non-procurement areas. This would seem to rule out Tom Ridge. It would, however, seem to rule IN Rob Portman.

It would also seem to rule out Mitt Romney but rule in David Petraeus. (You might think that Petraeus, as a general, would not be familiar with governance. But Petraeus, as a succesful general, has the clout and credibility to take on the Defense appropriation establishment big-time, and this establishment is one of John McCain's biggest bogeymen.) . It would rule out Mike Huckabee but rule in Joe Lieberman. But let's continue.

3.As BHO has picked a VP Who helps him to appeal to a major constituency that he himself seems unable to win -- working class White Democrats -- dso John McCain will pick a VP who, understanding the Washington budgeting process and having familiarity with Washington people and processes, helps him to appeal to our own equivalent of White working-class Democrats: our "Sam's Club Republicans," as they've been called. Actually, they're probably the same people that BHO hopes that Joe Biden will appeal to, but seen and talked to DIFFERENTLY. If I'm right that these are the voters who John McCain wants to use a VP to appeal to, we can now definitely rule out Mitt Romney but rule in Mike Huckabee. We can also rule out Meg Whitman, but rule in Tim Pawlenty. However, both Pawlenty and Huckabee have no familiarity with Washington: and if the last Governor to become President is any guide -- GWB -- we can see why John McCain will not choose a state governor. So who is left for John McCain to pick ?

4.There is Rob Portman. And there is David Petraeus. And there is Joe Lieberman. And so I think it'll be one of these three, in THAT order of probability.