Time’s Joe Klein has wise words (h/t Ross Douthat):
But if I’m a plain old white insurance salesman, I look at the Democratic Party and say, What’s in it for me? These feelings are clearly intensifying in this presidential campaign. They are bound to increase, perhaps dangerously, as the white electoral majority (currently about 70%) diminishes over time. If the Democratic Party truly wants to be a party of inclusion, it must reach out to those who are currently excluded from its identity politics. It needs to disband its caucuses. It needs to say, We are proud of our racial and ethnic backgrounds, our different religions, our lifestyle differences. But the things that unite us are more important than the things that divide us. We have only one caucus — the American caucus.
It seems to me this is the Democrats’ goal in slotting former President Bill Clinton in the primetime space customarily filled by the vice president or vice presidential candidate: to speak directly to that plain old white insurance salesman.
This was the original point of running with Joe Biden in the first place. The ’08 Obama campaign played up Biden’s working-class roots in Scranton, Pa., and his habit of commuting to Washington via Amtrak. Four years later, Biden’s usefulness in this regard has been outweighed by his habit of inserting his foot into his mouth.
Hence this week’s reliance on the “Big Dog,” as Clinton is affectionately referred to in Democratic circles. To have any realistic shot of unseating Obama, Mitt Romney needs two-thirds of non-college-educated white voters.
With Bubba’s help, Obama is trying to limit Romney’s share of that critical demographic.
Leo 
“Four years later,…”
I think it is less Joe Biden’s fault than the policy and political decisions of the Obama administration that are the main reason for Obama’s shakiness with the white American electorate. Specifically, his failure – and that of the Democratic Congress before 2011 – to investigate the hell out of and prosecute the financial crooks who are largely responsible for the economic mess. The failure to offer real assistance to the millions facing foreclosure. The failure to actually do something for unions (and the U.S. Postal Service). Not to mention the failure to change course on trade policy (over which both GOP- and Democratic-leaning pundits would of course go ballistic).
The Dems lost the Congress in 1994 largely due to NAFTA. A major reason why Clinton was able to leave office with high favorable ratings was because American workers had actually seen an increase in their real earnings for the first time in 20 years. We’ve gotten a lot of decisions like the former and damn few effects like the latter from the Obama (or Clinton III) administration.