He basically started the civil war because he thought he would "solve the issue of slavery" with the Fugitive Slave Act (which guaranteed federal over-reach), and instructed the Chief Justice of SCTOUS to rule in his favor, when it inevitably got hit with a lawsuit. This presidential support is also what allowed SCOTUS to just declare that blacks in America, even the ones who were free, owned property, or were even in political office, were just not considered citizens because something something English law something something, despite England actively ending slavery and having no objection to blacks in England. He additionally did nothing to stop the situation with Bleeding Kansas, and as the secession crisis deepened he neither pushed hard enough towards state's rights to keep the South in the Union, nor did he go hardline with the North, leaving everything entirely up in the air as violence increased. He did nothing to really even keep southern generals in the Union as the crisis worsened. He also presided over a massive bank failure. Oh, and he's famous for being a secret homosexual that took swims in the Potomac.

He was basically infamous at the time for being wrong about almost everything, and blew up the country.