Districting. There's a reason that the house has a typical 90% incumbent win rate -- most districts are very small, highly partisan areas that just don't change that much. There isn't a national wave strong enough to dislodge Nancy Pelosi from her seat representing most of San Francisco -- nor can even a double-digit Democrat win in Ohio defeat John Boehner when he's running unopposed. And, really, when they step down, they'll just be replaced by somebody exactly like them, because they represent their district. This is one reason nonpartisan redistricting should be mandatory -- it won't completely solve this problem, but it'd definitely help.