All I can say is the near-miss election of Jimmy Carter was and is quite likely a bullet dodged. Carter the man is a warm, caring sort, but Carter the public official seemed hopelessly naive, believing that merely setting a good example would cause others to fall in line. Foreign officials would have taken advantage of this for all they could, barring the presence of a no-nonsense national security advisor and a similar secretary of state (let's face it: add up all the players on the Democrats' side and you still didn't or couldn't come close to approximating Henry Kissinger). I can't imagine what he would have formulated as a response to the Soviet invasion of Afghanistan: a few tut-tut speeches, perhaps, and little more.
Further, he was well known as a notorious micro-manager while governor of Georgia: one wonders how he might have frittered away time better spent on more pressing issues--deciding who gets time on the White House tennis courts, perhaps?
A Carter administration would likely have been a dreary single term, full of pious sermonizing, lots of sentences that began with "you should..." or "we should..." followed by calls for lowering one's sights, sacrificing, and the like. It would not have been pleasant.