When Al Franken ran for Senate, his years as a founding writer on Saturday Night Light and as the author of books like “Rush Limbaugh is a Big Fat Idiot” were held against him. So once in Washington, he buttoned up his sense of humor.  Until now.   His new book is “Al Franken, Giant of the Senate,” and the cover is a portrait of Franken sitting in front of a roaring fireplace with his hand on a globe, a spoof classic senatorial imagery. Yet Senator Franken really has become senatorial over the course of his career. It was Franken’s question to Jeff Sessions in confirmation hearings, for example, that ultimately led to Sessions’ recusal from the Russia investigation.  David Remnick asked Franken about the the failed attempt to repeal the Affordable Care Act and the Russia investigation. Franken, the only elected official in Washington who has worked in show business longer than the Donald Trump, says he is not impressed by Trump’s skills with an audience. “I’ve never seen him laugh,” he says. The President “is like some fairytale, where if someone can get the king to laugh they’ll get half the fortune and the daughter.”