But only a small percentage of voters actually switched sides between 2008 and 2010. Moreover, there were almost as many John McCain voters who voted for a Democratic House candidate in 2010 as there were Obama voters who shifted the other way. That may be a surprise to some, but it comes from one of the largest longitudinal study of voters, YouGov’s Cooperative Campaign Analysis Project (C.C.A.P.), for which YouGov interviewed 45,000 people at multiple points during 2011 and 2012.

The results clearly show that voters in 2010 did not abandon the Democrats for the other side, but they did forsake the party in another important way: Many stayed home.

Fewer than 6 percent of 2008 voters in the presidential election voted for a congressional candidate from the other party in 2010, with the switchers roughly evenly divided across the parties, according to the C.C.A.P. It’s worth noting, however, that these switchers are not evenly distributed around the country, with North Dakota’s single district having very few cross-party voters (under 3 percent) and some Pennsylvania districts, for example, having upward of 10 percent switching between 2008 and 2010.