Bush’s two successful races, and the map on which he built them, are quite instructive when trying to understand Romney’s narrow margin for error this fall. In 2000, Bush won 271 electoral votes — one more than he needed to claim the presidency. In eking out that victory, Bush not only carried the South and Plains states with a near sweep but also claimed wins in swing states such as Nevada, Colorado, Missouri and the major electoral-vote prizes of Ohio and Florida. If Romney was able to duplicate Bush’s 2000 map, he would take 285 electoral votes — thanks to...