It was the secret force behind stories about John Edwards’s $400 haircut and Mitt Romney’s decision to put the family dog on the roof of his car. Donald Trump Jr. says it motivated him to meet with a Russian lawyer. We discuss the dark art of opposition research. Guests: Jonathan Martin, a national political correspondent for The Times; Ben LaBolt, the national press secretary for President Barack Obama’s re-election campaign. For more information on today’s episode, visit http://nyti.ms/2vF4L6w.