AFAIK, Graham keeps winning for only two reasons:

A) The Dems refuse to run a competent candidate
B) The primary field is so crowded that no *one* candidate can realistically strike a serious opposition. You have five different people all trying to attack Graham, and they all cancel each other out. Graham wins by default.

The last two cycles have been interesting in my congressional district in this regard. Chuck Fleischman is the incumbent (and retarded) congressman (R), but he had to fight for his life against a very well connected and savvy (but total douchebag) opponent in the primary in Weston Wamp. Wamp's an entitled little shite (his dad was the former congressman from this district), but he's smart, and the primary was essentially the only major election for this district's seat. The Dems didn't even bother to field a realistic candidate, despite the fact that Chattanooga proper is really pretty damn blue.

The rules are set up to support the incumbents. If you can find your way into office, with the way that primaries and gerrymandering have juiced the districts, you pretty much have a job for life.

This post was edited on 3/16/15 at 4:07 pm