For decades, the most powerful golf game in Washington has usually been whichever one the President plays. In the past five years, the capital’s power brokers have had almost zero luck joining it. Marvin Nicholson, meanwhile, has had the privilege 103 times since Barack Obama took office. Nicholson is not a Washington stiff. He is a former bartender and caddy who became John Kerry’s body man during the 2004 campaign after meeting the then-senator at a windsurfing shop. He now serves as Obama’s trip director, overseeing all aspects of the president’s travel. But his most important role is arguably as...