Addendum

I won’t fully repeat myself, but my arguments for why Andrew Johnson is the worst president in history and also making the case against Woodrow Wilson are here. To add a bit on Buchanan, essentially to qualify for the worst there has to be some combination of 1)inept performance and 2)bad policy/ideology. On the latter, Buchanan was an utterly generic Jacksonian Democrat, no more a slave to the Slave Power than any of the others. On the former, he was obviously pretty inept, but I have yet to hear any plausible set of actions that could have prevented the Civil War by that point — I think Pierce and Douglas’s work with the Kansas/Nebraska Act did more to cause the Civil War than anything Buchanan did.

Speaking of bad Jacksonian presidents, Van Buren is my candidate for “terrible president who is not identified as such often enough.”