Who's the worst president the US has ever had?

Depending on how the next four years go I'm on the fence between Bush Jr. and Trump but I'd like to hear from you

Edit:

Top 10 suggestions so far (unordered):

• Andrew Jackson
• Andrew Johnson
• George W. Bush Jr
• Ronald Reagan
• Richard Nixon
• James K. Polk
• Woodrow Wilson
• James Buchanan
• Franklin Pierce
• Donald J. Trump