Long before Michelle Obama became First Lady, her mother had misgivings about her marrying a young man named Barack Obama — because he was biracial. In a Chicago TV interview that aired during Obama’s 2004 U.S. Senate campaign — and newly resurrected by Michelle Obama biographer Peter Slevin in a book due out next month — Marion Robinson confessed to being “a little bit” wary about her future son-in-law being the product of a white mom and black dad. But it could’ve been worse, according to Robinson. “That didn’t concern me as much as had he been completely white,” Robinson...