Vice President Biden defends the administration's foreign policy --€” and questions Mitt Romney's ideas — on Thursday at New York University. Lucas Jackson/Reuters/Landov hide caption

itoggle caption Lucas Jackson/Reuters/Landov

Republican presidential candidate and former Massachusetts Gov. Mitt Romney speaks at a campaign rally in Tempe, Ariz., on Friday. Jae C. Hong/AP hide caption

itoggle caption Jae C. Hong/AP

Courting Tea Party voters in Philadelphia on Monday night, Mitt Romney speaks next to a large statue of Benjamin Franklin at the Franklin Institute. Tim Shaffer/Reuters/Landov hide caption

itoggle caption Tim Shaffer/Reuters/Landov

Rick Santorum won the Louisiana Republican presidential primary Saturday, beating front-runner Mitt Romney in the race to challenge President Obama. Jae C. Hong/AP hide caption

itoggle caption Jae C. Hong/AP

A screen shot of President Obama from the trailer for his campaign's movie The Road We've Traveled. BarackObama.com/YouTube hide caption

itoggle caption BarackObama.com/YouTube

Peoria, Ill., as seen from across the Illinois River. Jeff Haynes/Reuters /Landov hide caption

itoggle caption Jeff Haynes/Reuters /Landov