"I am taking this step because we have to repair the damage that's been done to our country over the last six years," Richardson said in a statement on his official Web site.
"Our reputation in the world is diminished, our economy has languished, and civility and common decency in government has perished," he said.
Richardson said the next president "must get our troops out of Iraq without delay."
"Before I became governor of New Mexico, I served as ambassador to the United Nations and as Secretary of Energy," he said. "I know the Middle East well and it's clear that our presence in Iraq isn't helping any longer," said Richardson.
Richardson became the eighth Democrat to announce he's seeking his party's nomination. Other Democrats in the race are: U.S. Sen. Joseph R. Biden Jr. of Delaware, U.S. Sen. Christopher J. Dodd of Connecticut, former U.S. Sen. John Edwards of North Carolina, U.S. Sen. Hillary Clinton of New York, U.S. Rep. Dennis J. Kucinich of Ohio, U.S. Sen. Barack Obama of Illinois and former Gov. Tom Vilsack of Iowa.
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