Buchanan was worst. He allowed his Secretary of War to ship Federal artillery to the south, where it could be used against the national government. The civil war was his creation.
FDR was second worst, for his inaction when Germany could have been stopped by very small forces, and his massive increase of government programs, which lengthened the depression, weakening the US when we needed to be strong. His agriculture programs, limiting US crop planting and food reserves, led to starvation of millions after WWII was over.
Wilson also is right up there, for is refusal to support the democratic nations, or to build up US defenses despite a world at war.
I would put Truman as 4th worst, for permitting Soviet opression in Eastern Europe, and publicly putting Korea outside the zone of interest, then being surprised when the communists accepted his offer.
Carter as 5th worse.
D
FDR insisted on making Henry Wallace VP for his third term. By the spring of 1944 FDR's health was so bad he could have died at any time...if he had died before the election Wallace might have been elected for a full term of his own, and there would have been no attempt to restrain the Soviets. Whatever Truman's shortcomings, we could have had someone much worse in place.
I was in college during the Truman administration. I opposed him, although I wasn't yet old enough to vote. However, as his term went on, I came to the conclusion that he wasn't as bad as I had first thought. In retrospect, he looks a lot better than Carter, LBJ, or even Kennedy.
I can't speak to Buchanan's presidency but I believe all the others (Bubba included) had some positive accomplishments as well as the troubles you mention. Carter on the other hand is credited with one accomplishment, that being the Camp David Accord. However, IMO that credit should be directed towards Sadat.