So the Confederate Constitution limits its presidents to single six year terms. After Davis, who would have the ambition and political clout to go for it in 1868, '74, and so on? Turtledove had Longstreet elected in '80, which I can buy, since he had a political career in the Republican party, but that still leaves quite a gap. If Lee was elected (not that I think he was much of a politician by inclination, but neither was Washington), he'd likely die in office, so his Vice President would be relevant too.