Jim Matheson, UT-02
Utah Republicans just won't give up on trying to redistrict Matheson out of his seat. In 2002, Republicans stretched his district out of Salt Lake City to give him the state's entire border with Arizona and a whole lot of Republican voters. Matheson hung on that year by a handful of votes and now has the most heavily Republican Democratic-held district in the country. GOP legislators are likely to try to take even more Salt Lake County Democrats away from Matheson, making his 2012 escape act even harder.
For more about the redistricting battles, National Journal and Hotline subscribers can check out Redistricting Central.