Obama had better alternatives to Joe Biden if he would have turned down the position (Tim Kaine, Kathleen Sebelius). If Obama chose John Edwards as his running mate, the election would be much closer but the odds are still in favor of the Democrats because of the economic collapse and the Bush gaffes (tax cuts, hurricane season, Iraq War, etc.). McCain agreed with Bush on most of the issues, which was a big liability. For McCain to beat an Obama/Edwards ticket, replace Sarah Palin with Huckabee or Pawlenty and have the McCain campaign aggressively attack John Edwards on his financial cover-up of his affair, illegal campaign contributions, and everything else he was tried and indicted for in 2011-12, but that's only if McCain can get his hands on that information. Edwards would not be helpful because Obama was going to win North Carolina that year anyway, Edwards was a one-term senator just like Obama, and Edwards would not be the attack dog that a running mate is expected to be. Instead, he'd probably be anticipating a run in 2016 (as was the case of 2004 with John Kerry at the top of the ticket).