Hate to break it to the political class, but the party had a tattered image a year before that when our Senate candidates got trounced along with the party favorite Romney. The House elections were neutral at best with redistricting that should have helped us gain seats.
It ain't a government shutdown that caused it. It's the failed leadership of our party that ruined a 2010 landslide at all levels and continued to bring absolutely no message voters and allowed their opponent to vilify them successfully with no response.
In the year before 2012, Obama's Gallup numbers were breakeven to positive 75% of the time and mid-single digits negative about 25% of the time. Prior to 2010, his numbers were negative by about 3 to 4 points during the last six months. In the 2014 cycle, Obama's numbers have been negative by about 10 points for the last 13 months. The White House's numbers have a huge impact on Congress. Bush single-handedly ushered in the Dems' lop-sided domination of Congress in 2006 with his lousy Iraq- and Katrina-related poll numbers.