Joe Dunford, the commandant of the Marine Corps, will replace Army Gen. Martin Dempsey, who will step down as Chairman of the Joint Chiefs this fall after four years on the job.The President praised Dunford, the former commander of U.S. and NATO troops in Afghanistan, in making the announcement in the White House Rose Garden.I know Joe. I trust him.He’s already proven his ability to give me his unvarnished military advice based on his experience on the ground.If confirmed by the Senate, Dunford will have a long list of challenges, including deep cuts to military spending,threats from cyber attacks and the spread of extremist groups across much the Muslim world.