Who is the "moderate Democrat" ? Dennis Moore is a down-the-line liberal who scored a 16% ACU rating in 2005 in a clearly GOP district. If the RINOs hadn't knifed the distinguished Vince Snowbarger, he'd still be the Congressman today. They're going to try to knife the equally distinguished Conservative Attorney-General Phill Kline this November with one of their apostates running as a 'Rat.
I've heard differently.
Snowbarger did nothing to distinguish himself in his one term in Congress, didn't come back to the district a lot and was a terrible fund-raiser.
You could lay some blame on moderate Republicans who were still disgruntled over over the 1996 primary between Snowbarger and Ed Eilert - but to lay the blame entirely on moderate Republicans is not true.
Compare Moore to the Nancy Pelosis and Harry Reeds of the party and he comes off as downright conservative. Moore makes sures that he votes with the Republicans on enough isses that he can seem moderate. He's with the party on the big ones, though.