Meh, I don't know how an already-ran candidate would be accepted by the Dem's that year. I'll agree that he could run, but I doubt he can win.
Yes, Carter in 1980 would have him running 6 years after leaving the Georgia statehouse. Hard to envision him getting the nomination when out of office so long.
I like Carter personally, and think he'd be okay as a peacetime President, but was too nice to be POTUS when he was. His ideal time period is 1990s, as a New Democrat; as a libertarian Republican, I don't buy into the whole "far-left lunatic Carter" B.S., although I do believe he was a weak and ineffectual president during his time in office.