According to multiple sources, including those folks who watch TV ad buys for a living, the first incumbent House Democrat to see the national party (DCCC) fully pull its financial support for TV ads is: Ohio Democrat Steve Driehaus.
Driehaus is facing a rematch with the Republican former congressman he defeated in 2008, Steve Chabot. Polling in this Cincinnati-area district this entire year had shown Driehaus behind Chabot. It's a district that in 2008 saw a surge in African-American turnout that many folks attributed to Barack Obama's name being on the ballot. Without the same level of support, it's an uphill battle for the freshman Democratic incumbent. But with the DCCC now out, it's fair to say the national party doesn't have a lot of confidence in its chances of Driehaus holding. In other words, he's being written off.
There are a number of Democratic-held House districts the DCCC will be making tough choices about in the next few days because if they want to pull BACK a buy they promised a specific TV station, there's no penalty if they do it in the next few days. It all depends on the market and the specific TV station's rules. In the case of the Cincinnati market, the DCCC had to make its final decision earlier this morning and that's how this news leaked out.
According to some well-placed sources, a handful of other Democratic incumbents will be experiencing this same feeling of national party abandonment later today as the news about the DCCC's ad buys leak out. Again, due to specific TV station commitments, the DCCC has to decide today if they are "in" or "out" in a number of races because if they are "out" then they can move that money without penalty.