The National Journal surveys the 2012 Congressional landscape and, inter alia, finds the Democrats at a distinct disadvantage because of redistricting:
Republicans have the ability to expand their congressional majorities in other battleground states. In Pennsylvania, unfettered control of redistricting will allow the GOP to draw a Democrat out of office. In Ohio, which will likely lose two House seats, Republicans will be able to better protect its five incoming freshmen, and probably will be able to force two Democrats (from the Cleveland area) to square off against each other.
Republican State Legislative Committee Executive Director Chris Jankowski estimated the GOP will gain between 25 and 30 additional House seats from the reapportionment and redistricting process alone, a number that makes it all the more difficult for Democrats to win back the seats necessary to retake the majority. Republicans already are slated to hold between 241 and 244 seats in the new Congress, their largest majority since 1946.
The picture in the Senate is no rosier.