Like many presidents before him, Barack Obama has turned to foreign policy in order to steady his shaky presidency. But the White House’s worldly ambitions aren’t easy to come by. Obama was unable to return from Korea with a new free-trade agreement. Currently, the Senate is holding up the president’s hopes for a new arms treaty with Russia. On the horizon there are even more complicated international problems: drawing down troops in Afghanistan and improving economic relations with China. On Thursday, Obama left for Portugal to meet with NATO allies about their support in Afghanistan.