Previous posts have noted that very few House members are in districts carried by the presidential candidate of the other party. At National Journal, Charles Cook reports:
But there is a second reason why there is less elasticity in the House. As House Editor David Wasserman of The Cook Political Report points out, notwithstanding all the Democrats in Obama districts and Republicans in Romney districts, the chamber has fewer swing districts altogether. Using The Cook Political Report’s Partisan Voting Index, which ascertains how the presidential voting patterns in each congressional district differ from the national average, we took a look at the 2004 and 2008 presidential-election results in congressional districts (the final PVI incorporating the 2012 results will be available in the next month or so), and compared them with previous years. In 1998, there were 164 swing districts, which we define as a district with a Democratic or Republican PVI of 5 points or less. The swing districts outnumbered the 148 solid “R” districts where Republicans had an edge of more than 5 points, and the 123 solid “D” districts where Democrats had an edge of more than 5 points.
The number of swing districts dropped from 164 in 1998 to 132 by 2000, to 111 in 2002, then to 108 for two elections (2004 and 2006). The 2008 and 2010 cycles both had 103 swing districts, and the total slipped to 99 in the 2012 cycle. Currently, 190 districts have a Republican PVI over 5 points, 28 seats short of a majority; 146 districts have a Democratic PVI over 5 points, 72 seats short of a majority. This PVI analysis points to the inherent presidential voting patterns on a congressional-district level and ignores the strengths and weaknesses of individual candidates.