10. Rep. John Barrow (D-Ga.): With Barrow’s district getting about 15 points more Republican — perhaps the biggest shift in the country that made the district one that would have gone 59 percent for Sen. John McCain (R-Ariz.) in 2008 — one might wonder why this doesn’t rank higher on our list. In short, it’s because Barrow is a survivor. Like Reps. Jim Matheson (D-Utah), Dan Boren (D-Okla.) and Mike McIntyre (D-N.C.), Barrow has shown he can survive in conservative territory in spite of the ‘D’ next to his name. The reason Barrow is on this list and the others aren’t is that his district just got so much tougher.

9. Rep. Ann Marie Buerkle (R-N.Y.): Buerkle won this Democratic-leaning upstate district by a razor-thin margin in 2010 — and it got about a point tougher in redistricting — but she hasn’t shied away from partisan warfare in Congress. The man she beat, former congressman Dan Maffei (D), is hoping to use her opposition to the health-care law and her support for Rep. Paul Ryan’s (R-Wis.) budget against her. If any race is a referendum on those policies, it’s this one.