https://www.brookings.edu/articles/t...rymander-myth/
The gerrymander myth
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So why do so many well-informed observers believe that House elections structurally favor Republicans? The short answer is that until recently, they did. Here are the results of the four elections in the Tea Party era:
Democrats Republicans Proportional* Actual Difference
2010 44.9 51.7 233 242 +9
2012 48.8 47.7 215 234 +19
2014 45.5 51.2 230 247 +17
2016 48.0 49.1 220 241 +21
What changed? Two hypotheses fit the facts. First, Republicans caught Democrats flat-footed in the redistricting that followed the 2010 Census. Putting together a powerful plan called REDMAP, Redistricting Majority Project, they used sophisticated new software to gain Republican seats and translated their strong showing in state gubernatorial and legislative elections into district lines that favored their candidates.
And second, because Democratic voters were more geographically concentrated in urban areas than Republicans were in the rest of the country, Republicans could more efficiently translate votes into House seats than could Democrats, who won supermajorities in urban areas but lost contested elections elsewhere. This made possible anomalies such as 2012, when Republicans ended up with a healthy majority of 234 seats, even though they lost the national popular vote.
