U.S. House Elections
Prior to the 2012 elections, the Republicans held 240 seats in the U.S. House, compared to 195 for the Democrats. After the elections, they held 234 seats, to 201 for the Democrats, a shift of six seats to the Democrats. The shift in the popular vote for the House between 2010 and 2012 was greater: Republicans won 53.4 percent of the two-party vote in 2010 but just 49.4 in 2012 (Jacobson 2013). Thus, Republicans were able to win a majority of the House seats in 2012 with a minority of the popular vote, as they benefitted from House district lines that more efficiently translated their popular votes into seats.
U.S. Senate Elections
Prior to the 2012 elections, the Democrats held 53 seats in the U.S. Senate, counting two independents who caucused with the Democrats. After the elections, they held 55 seats (again counting two independents who caucus with the Democrats), to 45 for the Republicans, a shift of 2 seats. Considering that Democrats held 23 of the 33 seats up for election — which meant that they had far more seats to defend than did the GOP — some observers considered the small Democratic gain to be noteworthy.
Election results for individual House and Senate races are available at CNN.com.