With one debate left, President Barack Obama and challenger Mitt Romney are retreating from the campaign trail to bone up on foreign policy, leaving the work of courting voters to their running mates.

Monday’s debate in Boca Raton, Fla., with its focus on international affairs, is the third and final between the two rivals and comes just 15 days before the election.

Obama left on Friday for Camp David, the presidential hideaway in Maryland’s Catoctin Mountains. He was to remain there with advisers until Monday morning. Romney was to spend the weekend in Florida with aides preparing the debate.

Romney running mate Paul Ryan planned a campaign stop in Pennsylvania on Saturday. Vice President Joe Biden was headed for St. Augustine, Fla.

Monday’s 90-minute debate will be moderated by Bob Schieffer of CBS News. It will be similar to the first debate, with both men standing at lecterns on a stage. Schieffer  has listed five subject areas, with more time devoted to the Middle East and terrorism than any other topic. While the economy has been the dominant theme of the election, foreign policy has attracted renewed media attention in the aftermath of the attack on the U.S. Consulate in Benghazi, Libya, that killed four Americans, including U.S. Ambassador Chris Stevens.

Obama had ranked well with the public on his handling of international issues and in fighting terrorism, especially following the death of Osama bin Laden. But the administration's response to the Libya attack and questions over levels of security at the consulate have given Romney and his Republican allies an issue with which to raise doubts about Obama's foreign policy leadership. Ryan told Milwaukee radio station WTMJ on Friday that the president was refusing to answer even basic questions.