According to the latest Public Policy Polling (D) poll (8/27-8/29, 724 LV, MOE +/- 3.6%), Richard Burr leads Elaine Marshall by a narrow 43 percent to 38 percent margin. This is especially troubling news for Burr, because incumbents below 50 percent in August rarely win, to say nothing of those below 45 percent.

The whole trajectory of this race has been bizarre. North Carolina leans Republican by a few points at the presidential level and is a fairly conservative state at the local level. Burr hasn't committed any unpardonable sin that would normally sink an incumbent below 45 percent. One would expect him to be well above 50 percent in this environment, even given the slow movement of the state back toward the Democrats over the past decade.

But North Carolina voters are notoriously hard on their incumbents. No Senate candidate has won more than 55 percent of the vote in the last 35 years, and no senator has been re-elected since Jesse Helms in 1996.

Ideologically, the state's voters aren't that different from Louisiana's: the liberal/moderate/conservative breakdown for North Carolina was 18/43/39 compared with 16/42/42 in the Pelican state. But North Carolina Democrats have done an unusually good job holding onto the state's moderate voters. In 2008, President Obama won 63 percent of moderate North Carolina voters, while he won only 45 percent of all North Carolina voters. These moderate voters are presently breaking 52 percent to 26 percent for Marshall, keeping her very much in the game.

The good news for Burr is that he's leading in every area code in the state, save for the Raleigh/Durham 919 area code. There are half as many undecideds there (8 percent) as in other regions of the state. This suggests some room for growth for the senator. But make no mistake about it: Burr seems to be having difficulty swimming with the Republican tide and looks like he is vulnerable this cycle.