Let's not fool ourselves into believing that Biden reinforces Obama's central message during the primaries: "change we can believe in." Nor does Biden symbolize a generational choice in the way that Al Gore was for Bill Clinton in 1992 – signaling the changing of the guard. No, Biden is the epitome of the Old Guard in Washington.
So why did Obama pick him? Because his team apparently recognized, just in time perhaps, that running a "post-partisan" campaign as an agent of change simply wasn't going to bring victory in November. Choosing Biden shows that the Obama team's reverence for a new politics has been mugged by reality.
That reality consists of two key facts: 1) Polls show lingering reluctance among white Democrats and independents to embrace Obama. 2) McCain's negative strategy is working.
Heading into the conventions, polls have pointed to the weaknesses in Obama's candidacy. It's not just white men, either. McCain's favorables are at least as high as Obama's, even in some states where Obama leads. In polls of generic match-ups between Republicans and Democrats for Congress, Democrats lead by double digits. Obama has no such lead – a signal taken by many that his support is not as strong as it should be, given the public's overwhelming rejection of the Bush presidency and Republican rule.
The bottom line: For all the factors that would seem to favor Obama and the Democrats this year, the race is a tossup, and the outcome is going to be very close.