One clear fault line comes on defense spending. Romney has vowed to spend at least four percent of gross domestic product on the military, which could add more than $2 trillion to the defense budget over a decade. Mr. Obama has attacked Romney for advocating spending money the military says it doesn't need. But the promise holds appeal to defense contractors and other military stakeholders and could help Romney win votes in Virginia and other states with a significant military presence.

One wildcard, meanwhile, will be how the candidates handle a New York Times report over the weekend which, citing administration officials, said the U.S. and Iran had agreed to one-on-one negotiations over Iran's nuclear program starting after the presidential election. The White House denied a final agreement has been reached. While the report would seem to signal progress in curbing Iran's nuclear ambitions, Romney could portray Iran's promises of talks after the election as an empty gesture designed to buy time.

Both candidates have sought to portray themselves as "tough on China" and their opponent as weak. Romney has said that unlike the Obama administration, he would label the nation a "currency manipulator" on his first day in office. The counterargument being made by the Obama administration, said Dr. James Lindsay of the Council on Foreign Relations, is that "[d]eclaring China a currency manipulator is likely to boomerang on the United States because China has multiple ways to retaliate."

Of course, choosing a side on that particular issue and many others requires a level of foreign policy understanding that most Americans don't possess. (Says Lindsay, diplomatically: "It's safe to say that knowledge about various foreign policy issues varies widely across the public.") For the candidates, the details may be less important than the presentation: Most Americans may not know where they stand on exactly which sanctions should be put in place against Iran, but they do want to feel as though their president is both strong and smart on the world stage. O'Hanlon argues that "Romney has the harder hand to play" in the debate because Mr. Obama has clear foreign policy victories on his resume -- ending the Iraq war, capturing bin Laden -- along with relatively few missteps.

"Obama's in a good place to play a good solid defensive hand," he said. And the president is poised to play it: Asked last week about his debate strategy for Monday, he quipped, "Spoiler alert: We got bin Laden."