I'm sad to say that he came to my mind, too. Sad because that's the caliber we need, but I don't see anyone like that in the world of politics. Might be someone, but no one well known.
A decade or so ago, Kucinich might have been that person.
Obama might be the closest, but he can't run.
Of those running, I think Bernie and Lizzie are closest programmatically - by which I mean that they want to heal the nation - but don't have Carter's demeanor.
Pete may have the best demeanor, but lacks the sincerity that Carter had (or that Bernie and Lizzie have). I think Booker probably has the sincerity, but lacks the demeanor.