Dubya's Worst Years - 2000,2001,2002,2003,2004,2005,2006,2007 and 2008.

There were more than five deadly blunders/criminalities by him of course but the five worst were:
1 The war on Terror
He squandered an enormous opportunity to unify most of the world behind an international effort to stop terrorism. Bush took, in the wake of the attacks of September 11, 2001, the greatest worldwide outpouring of goodwill the United States has enjoyed at least since World War II and threw it away by insisting on pursuing a foolish go-it-almost-alone(with a few lapdogs)invasion of Iraq, thereby transforming almost universal support for the United States into worldwide condemnation.

2 'Pre-emptive war'
He promoted the concept of "pre-emptive war." Bush misled (to use the most charitable word and interpretation) the American public about weapons of mass destruction and supposed ties to al-Qaeda in Iraq and so into a war that plainly (and entirely predictably) made the United States less secure, caused a boom in the recruitment of terrorists, killed American military personnel needlessly, sucked up almost all the nation's available military forces and became a bottomless pit for the money of American taxpayers. And, through all of this, he set a terrible precedent for other nations to launch wars.

3 Disastrous Economic Policies
He pursued disastrous economic policies that have resulted in a concentration of wealth and income at the very top and thrust the United States and the world into the worst economic collapse since the Great Depression. Bush inherited an annual federal budget surplus of $230-billion and transformed it into a $500+ billion deficit. He sharply reduced taxes on the very wealthy, helping to return the income shares going to the hyper-rich to the levels they had last reached at the end of the 1920s. This, combined with his opposition to regulation, has led to a reprise of 1929, along with a massive debt to be passed on to future generations.

4 Subverted his own constitution
In the name of "security," Bush severely curtailed the very freedoms that the US military propagandists say they are fighting to defend. Proclaiming himself to be a conservative, he maintained that big government should be able to run roughshod over the Bill of Rights, and that the government must have all sorts of secrets from the people, but the people can be allowed no privacy from the government. He played directly into the hands of Osama bin Laden by changing the United States in ways far beyond anything the terrorists could have accomplished directly on their own. He endorsed torture and holding people prisoner without charges. The list goes on.

5 Hurricane Katrina
Bush demonstrated the total incompetence of his administration through his and its utter failure to respond to one of the worst natural disasters in United States history, Hurricane Katrina in 2005. He looked the other way while a great city, New Orleans, drowned and then praised the incompetent cronies he had appointed to deal with disasters, even as they utterly mismanaged the situation.