Worst president ever?

I can think of only two Presidents whose actions and inactions were ultimately capable of destroying the United States: James Buchanan and George W. Bush. It's arguable that Buchanan was boxed into a corner: in the late 1950’s, nobody could have prevented the Civil War. Bush, on the other hand, has chosen to:

• Destroy the United States' fiscal integrity, accelerating the risk of a financial collapse that we will not be able to recover from
  
• Dramatically weaken the U.S. military, making it virtually impossible to address serious threats to the nation elsewhere, or project a credible threat to potential adversaries
  
• Dramatically weaken America's ability to project soft power around the world, while at the same time weakening institutions of global cooperation that -- if they had been strengthened instead -- could have been invaluable tools for protecting America's safety and interests
  
• Ignore (and in many cases, worsen) the threat of nuclear proliferation
  
• Seriously damage the institutions of American democracy, and implement infrastructure that could be used by future Presidents to virtually eliminate citizens' liberty (assuming, that is, that it is not already being used to this end)
  
• Make it financially impossible to solve problems ranging from healthcare to education, or to respond to a serious recession
  
• Weaken America geopolitically vis-a-vis China and the other world powers who are lending us the money we increasingly need to survive
  
• Fill the government with right-wing religious fanatics who are damaging one of our few remaining areas of competitive advantage: science and technology
  
• Systematically ignore (and in some cases worsen) problems of global sustainability at a moment in history when they might still have been addressed successfully
  
• Transform America's image so that many of the world's most intelligent, innovative people now choose to go elsewhere, while American companies must hide their identities to avoid losing market share
  
• Lose an entire American city -- New Orleans -- by replacing a competent emergency management bureaucracy with a collection of hacks
  
• Oh, and yes, Iraq: Unleash chaos in the Middle East, through a strategic blunder rarely if ever matched by an American president, making it easier for terrorists to recruit worldwide, strengthening the mullahs in Iran, and virtually guaranteeing horrific blowback over generations to come (while at the same time costing the nation $2 trillion and the lives of thousands of its bravest citizens, and profoundly damaging tens of thousands more)

All his fault singlehandedly? No. Many of them, however, are. The rest, he has actively worsened, either through ignorance, incompetence, ideology, or a combination of all three. Before George W. Bush, it would have been inconceivable that one President could do this much damage. Only history will tell which of these will be our undoing, but we'll have to be preternaturally lucky to dodge all the wreckage this man has unleashed upon us.