Buchanan's leadership, or more correctly his near total lack of leadership, is generally cited as one of the primary contributing factors to the outbreak of the Civil War. He refused to take a stance either way or undertake any action on the question of slavery at a critical moment in American history, deliberately kicking the can down the road to whoever was president after him, which turned out to be Lincoln. By the time Lincoln took office, years of inaction had allowed tensions to spiral out of control and effectively guaranteed the occurrence of the Civil War, when careful statesmanship years earlier may have prevented the worst.

Nobody's taking Buchanan's spot at the bottom until they manage to split the country in half and get 2% of the American population killed in an armed conflict again, which would be 6.7 million people right now.