Carter's chances are better than Nunn's at this point.
They always were.
If Nunn loses, she'll go for Isakson's seat in two years, whether he retires or not.
She won't. Her funds would be exhausted by then, and going up against a well-funded, popular incumbent in an (atlas) Blue state during an election year is much harder than going up against a bruised opponent who just survived a competitive primary. Nunn is likely to lose that latter contest anyway.
Let's say he retires, since he is about the same age as Saxby. That's a fun name. What then?
If we get another open seat in 2016 then the GOP primary is going to be rather chaotic like the one that happened this year. I could easily see Kingston making another go in 2016, maybe Handel as well.
If Nunn loses in 2014 (and I suspect she will, and not by a respectably close margin either) then the Democrats better wise-up for their own good in time for 2016. Its no use wasting resources in ruby red Georgia during a presidential year when there will be much more vulnerable Republican incumbents up in states like Pennsylvania, Illinois and Wisconsin.