First one I thought of when I read that. If (and there cannot be any doubt) Hitler was our worst leader, WIlli II was the second worst. Very similar personality as Trump btw., narcissistic, ego-driven, vindictive, incorrigible, pompous and an idiot with Dunning Kruger complex to boot.
ETA: notable third place: Hindenburg, who had already played an infamous role in WW II and its aftermath as commander-in-chief, and who as Reichspräsident paved the way for the nazis taking over.