In a comment, Recon asked about James Buchanan. The low marks I give him do not relate to his actions in response to the secession crisis at the end of his presidency. In all fairness, the guy was leaving office, tried to send the Star of the West to relieve Fort Sumter, and did nothing to prejudice the options of his successor, whose problem this clearly was going to be.
No, my problems with Buchanan lie elsewhere:
[I] . . . am confident that James Buchanan (1857-61) is at or near the bottom of the barrel. After having improper communications with the Supreme Court in connection with the Dred Scott case, he handled the Kansas Lecompton Constitution dispute in the worst possible way, stubbornly refusing to take advantage of several opportunies to diffuse the crisis. In the process, he went out of his way to alienate and destroy the credibility of Stephen Douglas, the last best hope of the Democratic Party. He somehow managed to believe both that secession was unconstitutional and that there was nothing he could constitutionally do about it. To top everything off, until the waning months of his presidency his administration harbored the likes of Secretary of War John B. Floyd, who was both corrupt and actively working against the federal government.
Kenneth Stampp's excellent America in 1857 is particularly damning of Buchanan's handling of the Lecompton issue.