According to an internal poll of Mick Mulvaney's discovered by National Journal, the South Carolina Republican has gained 11 points on 14 term Democrat John Spratt of the 5th district.
If the Chairman of the Budget Committee can't use his seniority to keep his seat safe, then I would expect to see a wave nationwide.
Public Opinion Strategies shows Spratt up 43-41 (MoE 5.3), so I show a 42% chance that Mulvaney's even ahead at the moment. Considering National Journal says the previous poll put the race at 48-35, for an 11% chance the Republican led, this is a huge move should it hold up in later polls.
National Journal notes that Barack Obama's favorability ratings are dropping, and doing so disproportionately among swing voters, making any overall reading of the President misleading as to the state of the race:
In the district, Pres. Obama's approval ratings aren't going to give Spratt a boost; just 45% approve of Obama's job performance, while 52% disapprove. Then again, that number is disproportionately high among African American voters, who make up 31% of the district. Obama's approval rating among persuadable voters -- largely white voters who gave McCain a 53%-46% win in the district -- is much worse.
This is an effect we will have to watch for throughout the South.
I also think it will be interesting to watch the NRCC and DCCC to see if and how they react in this district. That will be telling as to whether they have corroborating evidence that the race is this close.