They probably shouldn't discuss Europe or much of the rest of the world, either, at Monday's showdown in Boca Raton, Fla.
That's because it's nearly impossible to separate foreign policy from the American economy. What happens over there bears directly on jobs and living standards over here.
Tensions in the Middle East can send gasoline prices soaring. Recessions in Europe are pummeling U.S. manufacturers. And a trade war with China — the world's second biggest economy — would carry huge risks to both nations.
China is both the world's leading exporter and the United States' largest creditor.
Still, both Obama and Romney are taking swipes at Beijing. Romney says he'd tag China a "currency manipulator" if elected. The Obama administration recently has rolled out a series of restrictive measures against Chinese products and investment.
Neither man wants to look weak on China. And China bashing long has been a staple of American presidential races.
Yet no less an old China hand than Henry Kissinger suggests anti-China rhetoric from both candidates is "extremely deplorable" in such fragile economic times and with leadership in both nations in transition or up for a vote.
A conflict between China and the U.S. would be "a disaster for both countries," says the 89-year old former secretary of state. "It would be impossible to describe what a victory would look like."
In the U.S., opinion polls peg the economy as the No. 1 concern of voters.
Obama implored attendees at a boisterous campus rally in northern Virginia Friday to make sure to vote. "I want to finish the job," he said. Romney and running mate Paul Ryan were campaigning together in Florida.