Change of Stripe

Listening to Fox News Sunday this morning on the health care debate, I found an interesting change of stripe revealed. The question was to Senator Conrad, after discussing the potential of a "public option". The change of stripe was revealed when the host Chris Wallace asked Senator Conrad how moderate Democrats like him were going to reconcile their thinking with liberal Democrats like Senator Specter. 

Isn't this the same Arlen Specter who until recently was a Republican? How can someone with such long experience in the Senate and such a lengthy political career in general go from an "evil" Republican to a liberal Democrat in such a short period of time? (By the way, what does this say about the political affiliation of Sen Snow, based on her recent voting record?)