Undeterred by the embarrassing failure of his troops to find the weapons of mass destruction that formed the basis of the war, Bush on Thursday claimed the invasion thwarted future plots against the US by "madman" Saddam Hussein.
"Saddam Hussein was a gathering threat. He possessed and he used weapons of mass destruction," the president said.
"I was not about to leave the security of the United States to the desires and hopes of this madman," Bush added.
The president also sought to counter criticism over the high US jobless rate by stressing that he inherited an economy that was sliding into recession, which got worse still by a string of corporate scandals and the September 11 attacks.
Before speaking at a fundraiser for a political ally in Kentucky, Bush delivered the same message to friendly crowds during two stops in New Hampshire.
"Saddam Hussein was a gathering threat. He possessed and he used weapons of mass destruction"
Aides said the president was fighting back against opposition Democrats who have increasingly been vocal in criticizing the president for his policies on Iraq.
Bush, who offered no new arguments to justify the war, has accused the mainstream media of fueling unhappiness with the situation in Iraq by focusing more on the bad news from the war-ravaged country.
"We are making good progress in Iraq. Sometimes its hard to tell when you listen to the filter," the president said earlier.
With next year's presidential elections not too far away, Bush has been at pains to explain the rising casualties and costs of the war on Iraq.
Up to 93 US soldiers have died in Iraq since the president declared the war over on 1 May.