Republican Romney will seek to erode the Democratic president’s advantage on national security and try to emerge as a plausible commander-in-chief as they spar on Libya, Syria, Iran, China and the US stealth war on terrorism.
Obama’s camp signaled before the showdown in Boca Raton, Florida at 9pm (0100 GMT) that he would boast of ending a decade of costly US wars abroad, while Romney is set to charge that the president’s foreign policy is unraveling.
The rivals are neck-and-neck in national polls after Romney surged following his first debate win in early October and started chipping away at Obama’s foundation in the swing states that will decide the election.
Foreign policy is unlikely to decide who wins on November 6, with the sluggish economy driving the election, but Romney is under pressure to show basic competence following a string of blunders.
His campaign warned going into the debate that the United States could not afford four more years of Obama diplomacy if the president is re-elected.
“America stands weakened around the world, with our safety threatened, our allies increasingly isolated, and hostile nations emboldened,” Romney spokeswoman Andrea Saul said.