Never-ending war. The struggling economy. The impending electoral shellacking. With so much weighing on President Obama these days, so much dreariness and gloom to dwell on, a little levity here and there is a vital part of keeping the president from falling into a spiral of despair. That's why it has recently become a favorite pastime almost de rigueur at this point for friends and visitors to the White House to playfully sneak up behind Obama as he works at his desk in the Oval Office or strolls through the grounds. Nobody knows how it started, but it's a custom that has become popular with senators, advisers, and, particularly, Vice-President Joe Biden. The longer you can creep behind Obama without him noticing, the greater your bragging rights. The current record is held by General David Petraeus, who once shadowed Obama for three hours in a pair of wrestling shoes.