Arlen Specter left the GOP because it is a lot easier to win in Pennsylvania as a Democrat than as a Republican. It is that simple. For folks on the Right to brush this off as some sort of 'good purge' is extremely naive.
One could argue the GOP made no progress on limiting government in their four years of total control from 2002 to 2006. If anything, government expanded like never before.
We can't ignore initial Democrat polling, which shows Ken Lucas already ahead of Geoff Davis. And the GOP brand is getting killed right now in the Cincinnati media market, which might offset the automatic GOP advantage this district gives to Davis.