Former president Barack Obama sprinkles his new memoir with some kind words for his onetime wingman Joe Biden. “Joe had heart,” he writes in “A Promised Land.” “He had endured unimaginable tragedy. . . . Joe was decent, honest, and loyal. I believed he cared about ordinary people.” But haven’t we heard all this before? In one form or another, Obama has uttered these plaudits again and again. Over eight years, he and Biden forged a historic White House friendship: No president and vice president had ever grown so close and demonstrated such affection for each other. If anyone could provide special insight into our new president-elect, Obama surely would be that person. But you won’t find much enlightenment on Biden as presidential buddy, or as incoming Oval Office occupant, in the pages of Obama’s memoir.