Five things to watch for when President Barack Obama and Republican nominee Mitt Romney debate foreign policy tonight:1. THE TIEBREAKER: Romney ran away with the first. Obama edged him in the second. Stakes are high for their third and final showdown. Does that mean a repeat of last week's ornery tone? Or will the gravity of the issues -- war, terrorism, world leadership -- inspire more dignified discourse?2. REMATCH ON LIBYA: It sparked one of the hottest exchanges of the second debate. And there's more to it than when Obama called the consulate attack an "act of terror.'' Expect to hear about failed security, intelligence lapses and the Obama administration's shifting account of what happened in Libya. After Obama's parry last week, Romney gets another try.3. ROMNEY'S TEST: The former governor and businessman has limited foreign policy experience. He took hits for comments that ruffled British and Palestinian leaders last summer, and for hastening to criticize the administration's response even as chaotic events were unfolding in Libya and Egypt. This debate is the prime moment for Romney to display the knowledge and judgment to lead on the world stage. 4. ON DEFENSE: Obama must defend four years of foreign policy. Expect Romney to accuse the president of weakening America's world leadership by mishandling Iran's nuclear ambitions, the pullout from Afghanistan, the Syrian conflict and the U.S. relationship with Israel. Can Obama rebut that criticism and focus on ending the Iraq War and killing Osama bin Laden?