Starting in May, at one of his monthly concerts at Madison Square Garden, Billy Joel began dedicating his song "The Entertainer" to Donald Trump. Before a show this week at Boston's Fenway Park, Joel explained why to WGBH radio hosts Jim Braude and Jared Bowen. "I am an entertainer, and I'm in the entertainment business, and in my opinion, Donald Trump's political campaign has been very entertaining," he said.