That's not quite true. Regular Civil Service protected by tenure can be fired, but it takes immense time and effort on the part of the supervisor and the cards are all stacked in favor of the employee. There are a thousand ways a clever employee can throw it off the track. You can't just fire him because you don't like him, he's "disloyal", or he isn't doing the job you want the way you want it. Usually the problem is "solved" the easiest way by getting him transferred to some other poor schmuck's domain.
On the other hand, federal political appointees can be fired. But this Administration doesn't seem to have learned that trick yet.
Sad, but true.
There's no benefit to the administrator from firing a non-performing employee. The result is, they're just moved aside and someone else is hired to do their work.
State, the Pentagon, and the CIA can't send people into far-flung areas, however. Civilian employees at the Pentagon don't have many other places to work other than there, dittoes for State unless you send them to Liechtenstein or something, and the CIA people are, of course, pretty much located at Langley.
These people have been the source of the leaks since the beginning. Any time you see a New York Times story with "administration sources" you can almost bet it is from one of these moles.
It has been a real problem rooting them out, and Goss is making a huge effort. Only so much can be done, though, unless you catch them in the act.
I believe Bush knew from the beginning that he would have this problem. I personally believe Tenet wasn't going to be kept much longer until September 11 happened. Then the President had to make a choice: he could either dump Tenet and cause a turmoil in the agency while we were trying to get information on our attackers, or he could keep him and hope that patriotism would keep the CIA on track. I believe this worked until the Iraq insurgency started. At that time, the democrats and their minions in the CIA realized they could start leaking things and use the media's desire to undercut Bush to erode his poll numbers, helping set the stage for a supposed 2006 Congressional win.
I am convinced that there is something going on under the radar, and I am praying that the President is successful in defeating these disloyal people who care more about their party than their nation.