From the New York Times:
Mr. Obama does not like debates to begin with, aides have long said, viewing them as media-driven gamesmanship. He did not do all that well in 2008 but benefited from Senator John McCain’s grumpy performances. Mr. Obama made clear to advisers that he was not happy about debating Mr. Romney, whom he views with disdain. It was something to endure, rather than an opportunity, aides said.