WASHINGTON, DC – MARCH 14: U.S. President Barack Obama (C) accidentially steps on First lady Michelle Obama’s dress as they walk onto the North Portico before the arrival of British Prime Minister David Cameron and his wife Samantha Cameron the White House March 14, 2012 in Washington, DC. Cameron is on a three-day visit to the U.S. and he was expected to have talks with Obama on the situations in Afghanistan, Syria and Iran. (Photo by Alex Wong/Getty Images)