My first reaction is that this is good for Obama, politically, bad for Afghanistan, as good for defense as can be expected, and bad for Petraeus. (The CIA being impervious to reform, hardly rates a good-bad mention.)
Bad for Petraeus: He probably was exhausted after close to 10 years in the field, but he should have been JCS Chief. True, working in counter-insurgency requires a lot of facility with operational intelligence, so it’s not completely a fish out of water. But the CIA does much more well-hedged intelligence “analysis,” most of it bad, than it does actual intelligence-gathering and use. Petraeus has directed the war in two theaters, and deserves a chance to apply what he’s learned to the military as a whole. It’s hard to escape the thought that Obama is sidelining someone he’s afraid of politically, even though Petraeus has repeatedly disavowed political ambition. That’s why it’s
Good for Obama Politically: He can put a purported rival in a position to fail (who was the last actually successful DCI?), keep him from speaking with authority as he spends energy navigating a bureaucratic and political jungle. Panetta will probably be at home (enough) in Defense, and will be on the President’s side there.
Good for Defense: At least in terms of not having an empty suit or someone likely to wreck the place or take on unnecessary fights. Panetta’s not a fool, but he was in over his head at CIA. His job will be to manage the Carter-like hollowing-out of DoD, which Obama’s successor will have to fix. But he’s unlikely to roll over completely, and will at least bring an outsider’s eye to the job.