Democrats know that they have a problem. As our country has become more politically polarized, we have increasingly sorted ourselves geographically. As Michael Barone has noted, “Democratic voting groups — blacks, Hispanics (in many states), and gentry liberals — tend to be clustered in most central cities, many sympathetic suburbs, and most university towns, while Republican voters are spread more evenly around the rest of the country.” We see this after every election cycle in maps depicting outcomes by county that show America as a sea of red with islands of blue. Although Hillary Clinton won the popular vote for …