There is no question that Republicans have a huge advantage in the House. But there is a big debate about whether it’s because of partisan gerrymandering or because Democrats are gerrymandering themselves into urban, heavily Democratic districts. One reason the debate continues, despite a near consensus among political scientists, is because the “wasted votes” phenomenon is abstract and hard to illustrate. In a Sunday Review article in The Times, I argued that the Democratic problem was mainly because of the distribution of their voters, not because of partisan gerrymandering, but I didn’t have a chance to include one of my favorite illustrations of the Democratic problem: Pennsylvania. Pennsylvania is a state where Mr. Obama won by a clear margin but lost a majority of the state’s congressional districts. The state was heavily gerrymandered by Republicans, which lets them squeeze out a few extra districts. But the Republicans probably would have still had an advantage on a neutral map.
That’s because Democrats win the state with huge margins in Philadelphia and Pittsburgh that are all but wasted in House elections. Mr. Obama won those two jurisdictions with 83 percent of the vote in 2012. Mitt Romney, in contrast, did not win a single county by so much — and he only won 67 percent of the vote in the state’s most Republican counties with a population equal to that of Philadelphia and Pittsburgh.
The fact that Democrats do so much better in Philadelphia and Pittsburgh than the Republicans do in their best counties is responsible for the entire Democratic advantage in Pennsylvania: Mr. Obama would have lost if he had won 67 percent of the vote in Philadelphia and Pittsburgh. But although those additional Democratic votes gave Mr. Obama his victory, they didn’t yield a single additional district.