Kiss of Death. It's a plant to associate Romney with the (arguably) worst President in US history and away from Obama being in that exclusive club.
It's got to be a distraction. Carter knows if Obama gets 4 more years he will definately be off the hook as the worst president in the last 100 years (or longer). He also knows his approval is the kiss of death for a conservative, or so he would like it to be. Personally, I think Carter should have his mouth duct taped every morning when he wakes up for the day so we don't ever hear from him again.