According to Public Policy Polling's latest presidential approval survey, former presidents enjoy higher popularity rates today than they did when they each left office, including John Kennedy whose approval rating has shot up 59 percentage points since his assassination, Ronald Reagan (+30) and Bill Clinton (+28).
Out of the last nine presidents, Richard Nixon rates lowest in Americans' hearts with a 19/62 favorability spread, down followed by George W. Bush who Democrats despise even more. Nixon scores positively among voters identifying themselves as "very conservative" (37/36) while Republicans approve of Bush 79/16.
Jimmy Carter scored a solid 6th place out of 9, with an overall approval of 45/43. From PPP (emphasis mine):
Carter is easily the least favorite President of Republican voters from this time period at a 20/74 breakdown, faring even worse than Richard Nixon. Voters under 30 give him his best reviews and they get worse as you move across the age spectrum- in other words the people who actually lived through Carter's administration are far more likely to give him a thumbs down.
In other words, young voters don't know much about Cater other than the fact that he was a peanut farmer. What's most scary about these numbers is how young voters personally unfamiliar with Carter's policies are so much less likely to understand how crappy they really are and therefore not afraid to vote for someone with similar ideals. (Hence, President Barack Obama.)
One thing's for sure, the GOP better ramp up its education efforts if it ever hopes to capture this uninformed voting bloc.