The third and final debate of the US presidential campaign began on Monday, with Democratic incumbent Barack Obama and his Republican rival Mitt Romney due to discuss foreign policy. The candidates shook hands on stage at Lynn University in Boca Raton, Florida before their last head-to-head, which pundits said may prove decisive, as opinion polls predicted an extremely close vote on November 6. New broadcaster Bon Schieffer of CBS was moderator, choosing questions in six topical segments, beginning with a question on Libya and the changing face of the Middle East in the wake of the so-called Arab Spring revolts. Obama -- who brought the last US troops out of Iraq and ordered the commando raid that killed Osama Bin Laden -- has generally been seen as the stronger of the two on foreign policy in the early stages of the campaign. But Romney\'s camp has mounted a strong attack on the administration\'s more recent record, alleging that a deadly attack on the US consulate in the Libyan city of Benghazi showed that Obama had underestimated the extremist threat.