Karl Rove admits mistakes were made during the Bush years
The failure to find weapons of mass destruction in Iraq damaged President George W Bush's reputation, his former strategist Karl Rove says.
In his memoir, Mr Rove writes that he felt he should have done more to reject claims that President Bush lied about the existence of Saddam's weapons.
He called his perceived failure one of the worst mistakes he made.
But he described the achievements of the Bush administration as "impressive, durable and significant".
In his book Courage and Consequence, Mr Rove defended President Bush, saying that history would look favourably on the president's two terms.
He said the president did not knowingly mislead the American public about the existence of WMDs, and described the 2003 invasion as a justifiable response to the terror attacks of 9/11.
Al-Qaeda and Osama Bin Laden were behind those attacks, but the Bush administration linked Saddam Hussein to them to build support for an invasion.
"Having seen how much carnage four airplanes could cause, Bush was determined to do all he could to prevent the most powerful weapons from falling into the hands of the world's most dangerous dictators," Mr Rove wrote in his book, which is due out next week.
He also defended the Bush administration's response to Hurricane Katrina which devastated New Orleans and other areas in 2005.
President Bush was criticised for his praise of Federal Emergency Management Agency administrator Michael Brown when he said "Heck of a job, Brownie" amid scenes of chaos.
The comment was not borne out of ignorance and incompetence as critics claimed, but was a statement of encouragement for an official under pressure, Mr Rove said.
Mr Rove was at the heart of some of the biggest decisions made by the Bush administration - and some of the biggest controversies.
Mr Rove was the chief strategist in President Bush's two presidential election victories, a role that made him highly regarded by Republicans and reviled by Democrats.
Early in President Bush's second term, Mr Rove was promoted to deputy chief of staff in charge of most White House policy co-ordination, including matters ranging from homeland security and domestic policy to the economy and national security.