Michael Barone explains the Democrats' House problem:
Democrats have too many seats that are heavily Democratic—or, to put it another way, Democratic voters are heavily concentrated in too few House seats.
There's more:
in 2004 John Kerry won 80% or more of the vote in 19 congressional districts, while the number of congressional districts in which George W. Bush won 80% or more was zero. Similarly and even more starkly, in 2008 Barack Obama won 80% or more of the vote in 28 congressional districts, while the number of congressional districts in which John McCain won 80% or more was zero.
An article well worth your time.
