This:
Mr. Biden supported the 2002 Iraq war resolution and thus is at odds with Mr. Obama, who opposed the war from the start and has made his judgment on the question a centerpiece of his campaign.
Senator Obama's entire argument against Senator McCain's foreign policy experience is based on the "judgment" issue. JUDGMENT TO LEAD is the actual foreign policy slash commander-in-chief slogan. If Senator Obama picks Senator Biden, it totally undercuts Senator Obama's foreign policy and Iraq arguments -- and, consequently -- strengthens McCain's strongest 'pro'.
Josh thinks that Biden brings a pile of foreign policy experience, which is true. But at the expense of totally neutralizing Senator Obama's cred during the election. And whatever experience Biden might bring, it's tainted by his piss-poor Iraq vote -- not to mention the fact that if his Iraq vote undercuts Senator Obama on the campaign trail, there won't be any opportunity for Wise Man Biden in the White House.
So what does Senator Obama gain from Biden on the ticket? Some stump zingers maybe (ouch! stump zingers!). But that's about all.