Barak Obama choice of Joe Biden as his Vice Presidential running mate shores up what is actually Obama’s most obvious liability as a politician. Obama presents himself as a uniter and a healer, and his stance is organic. While he is not a wimp, Obama temperamentally avoids conflct and does not seem at ease with either anger or disdain, although he can be very good at being incredulous. Biden however, can go for the jugular, and do it with a certain amount of class and in such a friendly manner that you feel he is admonishing you as a friend.
So when John McCain continues his smears of Obama, (and he is very comfortable with both nastiness and contemptful, even rageful disdain), Obama can now remain above the fray. While its an age old role for a VP (Agnew comes to mind as a prime example) to take on the dirty work, Biden is especially adept at that kind of reparte.
Biden may well be able to connect with the lower income voters who saw Hillary Clinton as a working class hero, and be able to forecfully express his anger at the loss of jobs and homes that have been the hallmark of the Republican Party’s Borrow and Bankrupt style of economics. As the most knowledgable politician in DC on issues of foreign policy, he is also very well suited to pin the warmonger label right where it belongs, on the tail of the elephant. If, as expected McCain chooses Romney as his VP, the Republicans will have two of the nastiest candidates they could field, and the Democrats wil have two strong males who are comfortable with their convictions and confidant enough to not rise to the bait.