Throughout history, Republicans and Democrats alike have used the reshaping of congressional districts to increase the number of House seats they can win. What's different this time is that Republicans, in states such as Pennsylvania where they have control of the process, are focused instead on fortifying the seats they already hold. They are trying to bolster vulnerable Republican incumbents, including freshman legislators swept into office in the party's 2010 midterm tidal wave.
With Republicans so strong at the state level, their strategy of focusing on shoring up shaky seats gives Democrats a steeper hill to climb. David Wasserman, who follows House races for the Cook Political Report, estimates Republicans have lifted 20 to 25 once-vulnerable incumbents out of the danger zone, enough to transform the battle.
"When you can take about half of the freshmen that you elected and make the seats better, that's good," says Rep. Lynn Westmoreland of Georgia, the House Republicans' point man on redistricting. "The odds are very slim of the Democrats taking the House back."