He didn't say that ALL ex-military men are the worst presidents. He said that the worst presidents have BEEN ex-military men. There's a difference.

By the way, I don't necessarily think that Lincoln was a very good president, although it's certainly debatable. I think the fact that he commanded during a victorious war and the fact that he died in office combined to turn him into a saint after the fact, so to speak, but I'm not so sure that he was really all that good a president.

As for Andrew Jackson, he was a ruthless s.o.b. who murdered Indians wholesale, broke treaties, and stole their lands. I don't admire him one bit.

One more aside: The USA has also had some wretchedly poor presidents who were NOT ex-military men. How about Hoover and Nixon and LBJ?

Kennedy was an interesting case. He was a real Cold Warrior, and not necessarily such a good president...but....he had the ability to inspire people. That counts for a lot.