He underestimates Nixon. The man was supersmart and sported ruthlessness only rivaled by his paranoia. He hangs back and lets the others slaughter each other, occasionally moving in to knock off the strongest contenders if the opportunity to do so safely arises. The only issue is what happens when it's down to him and only a couple of others.
I think he ranks Lincoln too high, but Jackson and Roosevelt are certainly top 3 material. Of course if the other presidents have knowledge of this (the rules don't specify if they have foreknowledge of the presidents that come after them), others might try to knock them off early. If I'm in there I'm wanting AJ and TR out of the contest early and I'm going to convince others to assist in that.