The killing of Osama bin Laden is undoubtedly a crowning achievement in President Obama's tenure at the White House.

Yet one year after the president ordered the successful mission that resulted in the death of the nation's number one enemy, it's unclear how much of a boost Obama will receive in the fall.

As ebullient crowds filled the streets surrounding the White House in the late hours of May 1, 2011, it was easy to think the killing of the mastermind behind the worst terrorist attack on U.S. soil would ensure Obama a second term.