Middle East expert Juan Cole somehow has generated a top ten list from a complete list that I'm sure is longer than this blog page:

Bush's Top Ten Mistakes in Iraq during the Past 4 Years 10. Refusing to fire Secretary of Defense Donald Rumsfeld when his incompetence and maliciousness became apparent in the growing guerrilla war and the Abu Ghraib torture scandal. 9. Declining to intervene in the collapsed economy or help put Iraqi state industries back on a good footing, on the grounds that the "market" would magically produce prosperity effortlessly. 8. Invading and destroying the Sunni Arab city of Fallujah in November, 2004, thus pushing the Sunni Arabs into the arms of the insurgency in protest and ensuring that they would boycott the January, 2005, parliamentary elections, a boycott that excluded them from power and from a significant voice in crafting the new constitution, which they then rejected. 7. Suddenly announcing that the US would "kill or capture" young nationalist Shiite cleric Muqtada al-Sadr in spring, 2004, throwing the country into massive turmoil for months. 6. Replying to Baathist guerrilla provocations with harsh search and destroy missions that humiliated and angered ever more Sunni Arab clans, driving them to support or join the budding guerrilla movement. 5. Putting vengeful Shiites in charge of a Debaathification Commission that fired tens of thousands of mostly Sunni Arab state employees simply for having belonged to the Baath Party, leaving large numbers of Sunnis penniless and without hope of employment. 4. Dissolving the Iraqi Army in May, 2003, and sending 400,000 men home, unemployed, resentful and heavily armed. 3. Allowing widespread looting after the fall of Saddam Hussein on April 9, 2003, on the grounds that "stuff happens," "democracy is messy," and "how many vases can they have?"-- and thus signalling that there would be no serious attempt to provide law and order in American Iraq. 2. Plotting to install corrupt financier, notorious liar, and shady operator Ahmad Chalabi as the soft dictator of Iraq, and refusing to plan for a post-war administration of the country because that might forestall Chalabi's coronation. 1. Invading Iraq.