At first glance, Gov. Scott Walker’s re-election last month looks like a carbon copy of his victory four years earlier. He won the same kinds of voters. He won the same parts of the state. And he won with virtually the same share of the vote: 52.25% in 2010 and 52.26% in 2014. But on closer inspection, there is an important difference: Wisconsin is even more polarized today than it was four years ago. Based on almost everything we know about the Nov. 4 election, the state’s fault lines are deeper and more sharply defined, its voters are more divided...