(Barack Obama, Creative Commons)

Seems his busy schedule was the reason for his subpar performance. The New York Times reported:

Like other presidents, Mr. Obama’s debate preparations were hindered by his day job, his practice sessions often canceled or truncated because of events, advisers said. One session took place just after he addressed a service for the four Americans slain in Libya, leaving him distracted:

Advisers had seen two presidents during practice debates, one who had been listless and passive two nights before and another energetic and aggressive the next night. It turned out the former was the one who showed up in Denver… 

Mr. Obama’s alternating performances left aides walking off Air Force One in Denver looking worried.

Preparation is key for the next debate. The public thankfully has a short attention span, but if Obama flubs the second match-up with Romney, he runs the risk of derailing his campaign permanently.

Biden is up next in the vice-presidential debates this Thursday night, where he faces Ryan.