The GOP keeps making that point in order to excuse its illegal behavior. She wasnt undercover (as a spy overseas), but she was NOC (no-official covert). We also know that a reason she was a NOC was because she had informants in Pakistan that were keeping tabs on Islamic fundimentalists there. We dont know what her role was, but what we do know, what is undeniable, is that her name was classified for a reason. And that Bush betrayed this for political payback. According to Washington sources, ex-CIA director George Tenent was furious about the leak.
Its totally unexcusable (not to mention illegal) for ANY president to act this way. There are even Republicans like Arlen Spector and John McCain who agree with this. But once again, we see the president act in total disregard for American law. Incidently, some of those informants in Pakistan were murdered as soon as Plame's identity was made public. So obviously blowing her cover did have an effect on US National Security.
Lastly, the Judge in the Libby case has stated that the Fitzgarld indictment (which is sealed) makes several clear references that Plame was 'covert', and that Libby knowing blew her cover.
So Fitzgareld clearly has something concerning Plame's status as a covert officier.