a post
It seems to me that what you're looking for these days is a nominee who gives you a narrative that the media can embrace, more than one who gives you a slight boost in a swing state or region. Thus Gore was a good pick for Clinton in '92, even though they were both Southerners, because he reinforced the whole "New Democrats, new generation, new direction" theme that the press ran with throughout that election. Similarly, I think that Dick Cheney and Joe Lieberman helped their respective tickets in '00, even though neither Wyoming nor Connecticut mattered to the outcome: Cheney by lending necessary gravitas to a campaign premised on restoring honor, dignity and so forth; Lieberman both by being the first Jewish nominee and by having a reputation as a Clinton critic, which at once turned the dull-seeming Gore into a trailblazer and helped him distance himself from the Clinton scandals.

[H]ere's one example of what I mean: If Barack Obama wins the Democratic nomination, he has an interest in picking a Southern running mate (like Mark Warner, say) less because the pick might help Obama carry some Southern states than because the narrative that such a pick projects--a black candidate with a white running mate from the old Confederacy!--dovetails perfectly with Obama's "beyond our differences" appeal.
Isaac Chotiner