With the Obama campaign announcing a trip to Europe and the Middle East, it's not too early to speculate whom Obama might choose to join him. We might be assuming too much here, but let's do it anyway: Whoever, if anyone, goes with Obama, he or she will certainly vault into the top tier of VP potentials.

On deck for just such a trip are those potential running mates that make the most sense: Sens. Joe Biden and Jim Webb and possibly Bill Richardson. All three have strong national-security credentials and their presence on the trip could be played as constituting an advisory role. Which of course means that if Obama announced that he was bringing along, say, Claire McCaskill, eyebrows might rise.

Now imagine the furor if Obama invited Hillary to come along...

He could of course invite a bunch of folks or none at all. But it's becoming clearer that with Iraq inching ever closer to stability, Obama is going to have a problem come the general election. He probably won't alter his views on withdrawal more than he already has, but he needs to at least bolster those views with a hard-hitting national-security running mate. That ditches a whole bunch of folks and sets the spotlight on a few others -- Webb, Biden, and Clinton.