Kagen doesn't even have an opponent. GA-12 leans strongly Democratic, ie a seat that went for John Kerry in the South.
I don't expect all seats to have a set opponent at this point: the election is still a year-and-a-half away. I would be surprised to say the least if Kagen doesn't draw a legit challenger.
Next: GA-12 leaning strongly Democratic? The same way that a seat that (virtually) went for George Bush in New England would lean strongly Republican? Tell that to Nancy Johnson.
The GOP almost picked up GA-12 in 2006, when they were getting trounced everywhere else. Besides, Republicans almost won it in 2004, and they
did win it in 2002.
If that seat is "heavily Democratic," then Democrats are in more trouble than they even realize down south. GA-12 is trending heavily Republican, and it is only a matter of time before the GOP picks it up.