Commentary Magazine's Jennifer Rubin lists some of the blunders that have put Obama's campaign in the situation it finds itself in today:

• Reneging on his public financing promise: Had he not done that, he might have saved his New Politics reputation and avoided his current money woes.
• Going on the Magical Mystery Tour: Had he not done that, we likely wouldn’t have had the “I still don’t think the surge was worth it” interview, there wouldn’t have been the priceless Berlin rally footage and he might have spent the summer at home talking about energy policy.
• Nixing the townhalls: Had he not done that, he — again — might have sustained the New Politics moniker and could have kept the focus on domestic issues and McCain’s association with George Bush.
• Losing the opportunity of a lifetime: Had he not done the angry liberal routine in Denver he might not be trailing among independents by an unbelievable margin of 52-37%.

If you also consider the fact that neither Obama nor his running mate, Sen. Joe Biden, has been in a competitive general election race in ages (never for Obama, decades for Biden), then that might explain some of these missteps.