The debate here at Lynn University, moderated by Bob Schieffer of CBS News, was dedicated to foreign policy even though it veered occasionally into domestic issues, and it presented the last opportunity for the candidates to face each other before the Nov. 6 election. While international relations have often taken a back seat to the economy during the marathon campaign, whoever wins will inherit a world with increasingly complicated challenges, from the turmoil in the Middle East to a resurgent Russia to an emerging China, and Monday’s debate highlighted the vexing issues ahead.

For all its fireworks, the debate broke little new ground and underscored that the differences between the two men on foreign policy rest more on tone, style and their sense of leadership than on particular policies. Mr. Obama and Mr. Romney seemed to align on matters like withdrawal from Afghanistan, the perils of intervening in Syria and the use of drones to battle terrorists.

While they varied in degree, the heart of their clash rested on who would pursue the same national goals more effectively and ensure America’s enduring economic and security role overseas.

Chopping the air with his hand, Mr. Obama came armed with a host of zingers. He accused his opponent, sitting at a table next to him, of “trying to airbrush history” and of seeking to “do the same things we do but say them louder.” At times, Mr. Obama lectured and even mocked Mr. Romney on the details of certain policies, hoping to expose him as an uninformed pretender at the risk of coming across as condescending. Mr. Romney at times sat stiffly, his hands before him, back ramrod straight.