Ranking presidents, especially the worst, can be done by a number of different criteria. If you look at how unqualified they are, Harding would probably top (or is it bottom) the list. But I think the need for competency is a major criteria. In other words, how bad did a president's ineptitude hurt the U.S.

For Harding and many others, they did not have the opportunity to seriously damage the country, no matter how inept they were. If not for 9/11 G.W. Bush would have probably gone down on the lower end of the list (mainly for his damage to the economy), but not near the bottom.

1. Without question this is Buchanan. Maybe no one could stop the Civil War at that point - both sides were hardening in their positions. But his behind the scenes support for the Dred Scott decision, as well as many other actions, poured aviation fuel on the fire. And he made no effort to stop secession or actively protect federal supplies. This time, and Washington to Jefferson were the two times the country could have disintegrated. With Washington, Adams, and Jefferson we had statesmen who while not perfect, did a superb job of keeping the country together. With Buchanan we had someone who helped push the country from disagreement to war.
2. This is a closer call but I think Hoover was clearly worse than G.W. Bush. The depression could have led to almost anything. Probably not a breakup of the country, but we could have easily gone down the road of fascism, communism, or some unique form of populism. In any of these cases, it would have almost certainly meant a harder life for the people in this country and who knows what would have happened in WWII. Hoover was completely unwilling to realize that the depression was so unprecedented that it required trying new things. (In this way he is much like Bush in his unwillingness to learn.)
3. G.W. Bush is clearly third. I cannot think of another president (other than the two above) that has done anywhere near as much damage to this country. And unlike the first two, his ineptitude has damaged many other countries - although that may be more a function of the global economy. (And Smoot-Hawley under Hoover did help worsen the global depression). Taking away the political differences I have with Bush and concentrating just on his competence we have:

• He has trashed the U.S. economy. The economy has not grown because of his economic program, but in spite of it. Clinton left him the biggest surplus in history and he has turned it into a series of ever larger record deficits. He has made fixed entitlements worse with his drug plan while failing to address the biggest problems with existing entitlements (medicare & medicaid) and with social security had a proposal that would have put people more at risk while increasing cost. It's a sad day when the Democrats are the party of fiscal sanity.
• He has heavily damaged the moral standing of the U.S. with the war in Iraq. Not quite as much as Vietnam, but close. And much of this stems not from the decision to attack, but the unbelievable gross incompetence with which the wars was prosecuted. Standing by as the entire country was looted - with it all in living color on everyone's TV. Not realizing that the Abu Ghraib torture needed to be addressed quickly and with people at the very top fired was a disaster across the world.
• He has left this country defenseless. The Katrina disaster was the one we have faced so far. But the lack of security for chemical plants, ports, the food supply - in fact everything. Like everything else in his administration, politics determined funding so Wyoming got a ton of money and countries with lots of targets, which tend to be Democratic, got almost nothing. We will be attacked, there will be more natural disasters, and Bush has done nothing to stop it.
• He has violated the civil rights which is one of the core principals of what makes America Amercia. When citizens can be spied upon and imprisoned at the whim of the president, then we are no longer a democracy. We are a dictatorship. Granted we are not in a Stalinist police state. But he has gone beyond a balance of power to say he as President can do anything he wants to do and the only limit on his actions is his own self restraint.
• He has taken the political sphere and pushed it to the bottom. Granted he has had lots of help here and it started with the Republican assault on Clinton. But Bush/Cheney/Rove have done their best to make our political system as divided as possible. And those Democrats who do reach out tend to get screwed so bad, that there is no second time.
• He has shown an incredible inability to learn from his mistakes. Reagan & Clinton were masters at evolving their efforts as they learned on the job. They weren't perfect, but they improved on the job. The job of president requires that there be a constant effort to improve based on learning what works and what doesn't. Bush for whatever reason (his faith, an overprotective mother, a staff that won't tell him things aren't perfect) - seems totally incapable of learning. In his world there are no mistakes.

I could go on but I don't see any need to list out more. History will speak, first in 10 - 20 years, and then with more authority in 50 - 100 years. And when it does, G.W. Bush will go down as one of our worst presidents. The only questions is will he be 3^rd worst. I will admit I might be wrong and he will turn out to be worse than Buchanan. Only time will tell.

This is easy - Washington, Lincoln, and Roosevelt (FDR) in chronological order. Close seconds - Adams (1st), Jefferson, Jackson, Roosevelt (Teddy), & Truman. As to anyone post-Kennedy, it's too soon to say. And yes, Wilson is purposely left off this list.

This was originally posted in my blog at Liberal and Loving It.