From a reader:
Jonah – My favorite theory is that this country didn’t live up to Carter’s ideals during his term, especially so when it tossed him out on his ear, and all that hammering away for the homeless over the years has only hardened his dislike and distrust of America, attuned him to its shortcomings, and engendered sympathy in him for other world players who feel the same way, or worse. Sometimes the simplest and most obvious explanation is best. Hope you and yours have a Merry Christmas (and hope that wish isn’t a faux pas) and Happy New Year.
Update: From another reader:
A simpler explanation — Carter was a mediocre non-entity as a governor (I was there), which happened to be just what the American public thought they wanted for a President after years of Johnson and Nixon. The public soon realized their mistake.