Hands down the worst president is Buchanan. He failed to to re-iterate Jackson's threat to the secessionists, failed to reinforce the national army's position in the south, failed to re-locate any movable national assets to the north, and even inexplicably transferred military stores to the south into unsecurable, even unguarded positions.
Next worse would be Wilson, who should have kept us out of WWI, should not have put us into an explicitly fascist--nearly totalitarian--command economy, and thereby quite likely prevented WWII. Really, what business is it of ours if the Kaiser gains influence and German subs blow up British ships which are illegally carrying munitions? That's without considering the man's particularly virulent racism.
FDR is a mixed-bag, out of the four big calls he had to make--how to combat the depression and whether to fight Germany, Japan, and Russia--he abjectly blew the first call and clearly had no plans to make the right call on the last, no signs of a change of heart there. He was an adequate wartime leader, and finishes up mediocre--great deeds, little net good done.
I should mention in passing, J.F.K. screwing up the Bay of Pigs.
Johnson should have stuck with the armed village/counter-insurgent model in Vietnam, it would both have been cheaper and would have eventually worked, if only by having the south outlast the outside patronage which supported the North. Cambodia would just be a nice place to visit, not a killing field.
Carter is certainly among the worst, and for reasons well covered already.
What I hope is noticed is that these Presidents all have something in common--all are Democrats.
Among a certain species of fool, Abraham Lincoln is given a place as being a "bad" president. They cite many specious reasons to justify this, the lead being that he started or caused the Civil War. The only thing he did to bring about the war was to be elected and act as if he had been elected, something that brings no onus for the war onto him. The worst thing that can be said about Lincoln is that he took maybe longer than required to find the generals who would destroy the South's rebellion. It would have been better done sooner, if possible.
The shame of it is all the Confederacy's.
Some poster above claims we need to look at the economic causes of the Civil War war, and the chief "economic" cause of the war in fact depends on it's political significance for all it's punch--the North was exceeding the South in every economic measure of advantage, and it would soon have the influence in Congress to overrule the interests of the South as the South had once been able to extort compliance from the North, in trade for it's signing on to the Constitution and good behavior.
What the Civil War was about was that the interests--the individuals--who ran the South politically were determined to remain the biggest fish in their pond, if need be by unconstitutionally, illegally, violently, and unjustly making their pond smaller.
There is no truth or utility in complicating any explanations for it beyond that point.
To amplify that observation made about the really bad President's being all Democrats, there's a reason for that. The Democratic party has not had a good idea since the 1830's and it has not had a not had a new idea since the 1930's.
From the passing of the Founding generation, the leadership of the Democratic party has always been populated by persons who will never fail to re-amalgamate the party into a half-winning coalition of whoever they can throw together into a bare majority of contradictory constituencies--they are a party of no fixed principles, but solely a patronage party trading favors.
In the 1830's they abandoned the Founder's goal of the diminishment of slavery, and in the 1850's called even its derogation unacceptably inflammatory. After the war they were the re-enslaver's party, the Copperhead's party. In the 1930's they adopted the popularist implications of Keynesianism, and bought ten extra years of Depression for us.
Later we must thank the Democrats for taking the Republican originated civil rights bills and taking them to the unconstitutional unjust extremes of defacto race quota systems, and invented "rights" which depend on confiscated funds for their fulfillment--not the absence of government interference.
What Obama is doing now.
Absent decent performance as CiC in an existential war--the foment of which he may darn well abet by his incompetence--Obama will take his proper place as one of the worst Presidents we will have the misfortune to endure.
The Democrats rank again!
Regards, Tom Perkins
molon labe, montani semper liberi &
para fides paternae patri