He was bombing Iraq for the first time since 1998 in March 2001, 7 months before 9/11. The purpose was just to weaken Iraq's air defense around the no-fly-zone. This is also where he stated the WMD excuse. It set the tone for his entire administration, and made it clear well before the September 11 attacks that his goal in office was to kill Saddam Hussein, and he was prepared to use all the resources of the U.S. to do it.
Using all the resources of the U.S. to do it raised the debt to unprecedented levels and set the stage for the economic crisis. He doubled the national debt. He started with $4.5 trillion and ended up with $9 trillion.
Despite the country being broke, the bailouts happened under Bush's watch. Bush revealed his lack of understanding of the fundamental issues surrounding the economy in his "like a casino" speech.
He passed the USAPATRIOT act. This single act circumvents the 1st, 4th, 5th, 6th, and 8th amendments to the constitution (free speech, unlawful search and seizure/ requiring a warrant, due process and takings clause, trial by jury, cruel and unusual punishments).
The war in Iraq started out as a police action. Congress did not make it a legal war until well after the 60 days the WPR granted bush. There was an 8 month period where the war was honestly illegal and unconstitutional, although the actions of Congress made it legal and constitutional retroactively in October.
He turned the actions of Osama Bin Laden into an excuse to invade Iraq. Osama Bin Laden was not killed until Obama was president a decade later.
He turned on his own intelligence community when they did not cooperate with him. His administration outed an undercover operative for political gain.
Abu Gharib happened under his watch.
Guantanamo bay raised many questions about America's honoring of the Geneva convention, which put American POWs in other countries in jeopardy. It also raised legal questions we still can't answer. The way we treat POWs in Guantanamo means we lost the moral high ground when decrying the treatment of our POWs by war enemies.
His vice President informed the American people that voted him in that he wasn't interested in representing them in an interview with Matt Lauer.
He created a security theater department which is using billions of tax dollars today. The TSA was Bush's idea.
He surrounded himself with revolving door corrupt CEOs who abused the privilege of office to further the interests of their own companies, and is incapable himself of admitting a mistake. Ever. Even in a book he wrote years after the fact.
Basically, the man had no business being President of these United States, and to make matters worse, there are still many people who feel he wasn't even fairly elected to begin with.