Worst president ever? Hardly. I can point to a few presidents (*cough*Lincoln*cough*) who have done MUCH worse for the country than Bush could ever hope to do. But, to honestly rate him a president you have to look at the president's responsibility and go from there.
The president has 3 to 4 real tasks as figurehead. Those tasks are national defense, upholding the constitution, stabilizing the economy, and keeping the nation's morale up. Let's go through each individually.
National Defense - Honestly, he did his part here. We were attacked in probably the most shocking attack in US history with 9/11. Nearly immediately, he went to Afghanistan and took them out of power. That is what I call mission accomplished. Then, he took it a step further and established democracy in both Afghanistan and Iraq, something which both countries wanted to get out of their oppression. I may be vehemently against the war, but he did his part in keeping us safe for the most part. So, overall: B
Upholding the Constitution: Well, this is where he ****ed up the most. Simply put, Bush has destroyed the integrity of the constitution due to the Patriot Act, as penned by John Ashcroft, and the horrors of Guantanamo Bay. The US Government has established itself as a big bully entity that is no different from the governments we claim to opposed. The Patriot Act allows the US government to wire-tap without a warrant, arrest you without cause, detain you at will, and search you. Of course, the running excuse is "if you are doing nothing wrong, why worry?" This excuse is bull**** because how long until what you do becomes a terrorist act as decreed by the state. The state should not have the power to listen in or watch you at all times. Overall: F
Stabilizing the Economy: We are in a recession on the verge of a depression because Bush hired men who do not understand simple politics. Instead of vetoing congressional bills that spent more, he backed them, and the war in Iraq is costing us trillions of dollars annually. Overall: F
Keeping Morale Up: Bush has only managed to keep the nation united in it's hatred of him. He has successfully guaranteed a democrat president, which will like hurt our deficit even more, all because of his ego and desire for power. I'll give him credit that the national unity is considerably higher due to so many opposing him, but it's not enough. Bush, from what I read a few months back, has a 28% approval rate - that is LESS than Truman had once he dropped an atom bomb. Overall: F
Overall: F - Fact is Bush failed to do tasks which all presidents should be invested in doing what's best for the people, not for his own cronies. Bush is a little more than a figurehead, however, because he just serves those who have influence over him.