Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" (Times Books) and of the new book "Governing America" (Princeton University Press).

Princeton, New Jersey (CNN) -- Just as Mitt Romney secured the Republican nomination, President Obama launched his presidential campaign with a weeklong celebration of his foreign policy accomplishments.

He and others in his administration blanketed the airwaves to discuss the first anniversary of Osama bin Laden's death, and the president made a surprise trip to Afghanistan to boast that he had fulfilled his promises.

The president's campaign team rolled out a controversial ad that praised Obama for having made the decision to raid bin Laden's compound and went so far as to raise questions about whether Romney would have done the same. "Which path would Mitt Romney have taken?" reads the screen, followed by quotations and news stories about Romney criticizing the hunt for bin Laden....