Here’s the deal: every 10 years, population gains and losses are calculated and congressional seats allotted to each state are reapportioned. As things are shuffled around, district boundaries shift and lawmakers who represent one area might actually live in another one under the new lines. Eyes glazing over yet? Stay with me.
The process is where things start heating up. In many cases, state legislatures are charged with drawing up the lines, and the party in control at that level is usually at will to do whatever they want with districts held by political rivals. In the case of California, an independent redistricting commission drew up a map that forced several longtime lawmakers to retire, sparked racial spats in Los Angeles and opened up a lot of opportunities for the Democrats itching to reclaim the House this fall.
This year in statehouses across the country, Republicans controlling the mapmaking process shored up some of the most vulnerable freshmen members to make their races a little easier, and shaved friendly voters out of Democratic districts. Democrats returned the favor in states like Illinois.