The majority of Americans think the benefits have not been enough to justify the costs and consider the US casualties in Iraq unacceptable.
In a poll released by the ABC News/Washington Post on Tuesday, 53% of Americans surveyed thought the war was not worth fighting, compared to 45% who thought it was justified.
Commenting on the poll results, Mounzer Sleiman, an expert on US national security affairs, told Aljazeera from Washington that Americans were not sure about the true reason for the war.
"As the polls have shown, there is still an overwhelming majority suspecting the reason for war against Iraq, particularly when the declared aim shifted from depriving Iraq from weapons of mass destruction to spreading democracy," he said.
Americans who think the war placed the United States in a strong position fell from 52% during the height of the war to 28% now.
But 44% said they thought the Iraq war had improved
the chances of democracy in the Middle East, compared with 9% who said it had lessened the odds.
"Traditionally, Americans do not support military intervention and human losses in order to achieve aims like spreading democracy," Sleiman said.
The US public also does not have the stomach for battles elsewhere in the world: Nearly three-quarters of those polled opposed a military confrontation with North Korea to force it to give up nuclear weapons and also saw it as a threat to the US.
"There is still an overwhelming majority suspecting the reason for war against Iraq"
expert on US national security affairs
Two-thirds opposed military action against Iran, which Washington accuses of trying to build nuclear weapons.
When asked whether the withdrawal of US allies' troops from Iraq such as those of Spain, the Philippines and Italy would affect public opinion, Sleiman said: "It will certainly have an affect.
"I think the withdrawal of the Italian troops will have a great negative morale impact as the US forces will alone undergo losses. The withdrawal will also increase anti-war sentiment domestically."