That district voted 49% for Bush in 2004. I don't think they'll be taking too kindly to his public proclamations of guilt and military failures.
Western PA is a strange place. The people there are more conservative than, say, the midwest, but because daddy (or, more often now, granddaddy) worked for the union, they can't manage to pull the R lever. The D's are for the working man 'n'at.
His district is emblematic of that. If you abuse Murtha too much, they will tune out. They'll just figure the nice old man is being beaten up by meanie Republicans and they'll vote for him again. His district is also an older-skewing district that remembers the steel days fondly and are disconnected from the fact that their kids don't work in the steel mills anymore because people like Murtha made it too expensive to have steel mills in PA.
You must understand that you could show them videotape of Murtha saying something and they will believe he never said it if Murtha denies it afterwards.
I am a bit pessimistic about Irey's chances. It's an uphill battle, but she's really fighting. I think she can do it, but it will take a light touch and she has to play up every tick in the polls she makes. She has to make herself look inevitable and be a "sweet young lady".