At this point it's becoming more about Electoral College votes than the national popular vote or racial/ethnic or gender components thereof. It doesn't get much press, but Obama has had an electoral vote lead for weeks now. That's probably one reason that Obama's campaign has not been as aggressive as they might otherwise be - they don't want to make any mistakes.

With the Democrats already pretty secure with about 66% of the Hispanic vote and probably 90% of the black vote, they may want Richardson on the ticket to selectively secure the elctoral vote in southwest states where there are plenty of Hispanics. The black vote may make the Carolinas a battleground anmd Biden may help there a Kaine certainly might also. It gets pretty complicated.