One thing is clear: It's no accident that Obama beguiled the electorate (and maybe himself) by over-promising his ability to change Washington, end partisan gridlock and "part the waters," so to speak. He'd been practicing similar social jujitsu most of his life. [. . .] In "The Bridge," Obama's mother comes alive as a smart, stubborn idealist, a devoted but also practical globalist, a lifelong anthropology student who also held jobs at New York foundations and women's banking groups and did pioneering work in the now-mainstream field of microlending (as well as policy prep work for the United Nations' 1995 World Women's Conference in Beijing; in a time-travel cameo, Dunham had high hopes, Remnick tells us, for first lady Hillary Clinton's advocacy). She was a devoted mother who loved her son passionately, but nonetheless left him without her for large swatches of a sometimes-forlorn childhood. Clearly Dunham deserves her own biography. [...