As of 2015, experts consider the worst U.S. presidents in history to be James Buchanan, Warren G. Harding, Andrew Johnson and Franklin Pierce, according to a survey of presidential scholars. Public opinion polls compiled from 1996 to 2010 show that the public largely agrees with this ranking.
In general, presidents receiving the lowest rankings were not nominated for a second term, including Buchanan, Harding, Johnson and Pierce. The presidents ranked the highest won second terms, with a correlation between receiving a large share of the vote and being considered to be better presidents in history.
In the modern era, scholars consider the worst U.S. presidents to be George W. Bush, Richard Nixon and Jimmy Carter while opinion polls showed the same. Historians consider Franklin Delano Roosevelt, Harry Truman and Dwight D. Eisenhower to be the best presidents of the modern era.
Both historians and public opinion consider Buchanan to be the worst president due to his mishandling of the crisis between the North and the South over slavery and territory designation. Historians believe his policy of inactivity over the rising tensions predating the Civil War played a role in the onset of the war, as he brushed off potential conflict as one of little importance.