“I like you. You and me, we’re going to be best friends.” It is early January, and Eric Schneiderman is sitting in his 25th-floor office above Lower Manhattan, doing his best Donald Trump impression, puckering his lips into a duck face, scrunching up his nose and lowering his voice into something that resembles the president’s outer-borough growl. Schneiderman is recalling his meeting with Trump in 2010. Back then, Schneiderman was running for attorney general of New York, and Trump was still in his pre-birther, reality TV host phase. Trump had donated money to one of Schneiderman’s opponents in the Democratic...