Smith, Hedrick (2012-09-11). Who Stole the American Dream? (Kindle Location 6337). Random House Publishing Group. Kindle Edition.
In 2012, Republicans had built in such a huge advantage through manipulating district lines after the 2010 census that they won a 33-seat majority in the House of Representatives even though more people voted for Democratic candidates than Republicans (56 million to 55 million). In Pennsylvania, Democrats outpolled Republicans but the GOP won 13 seats to 5; in North Carolina, Democrats won the popular vote, but the GOP won 9 seats to 4. Michigan, too, saw a Democratic majority but Republicans got 9 seats to 5. In other states, Democrats did the gerrymandering. In Massachusetts and Connecticut, Republicans won one-third of the vote, but got no seats in Congress. It is a problem nationwide.
In fact, so many House districts have been gerrymandered that only about 40 of the 435 House seats are seriously contested in elections.