"He said we left Vietnam too soon," Biden told about 300 delegates attending the state convention of the Nevada AFL-CIO. "I don't know what planet he was on."

Biden said the United States was spending money "on the wrong things," and Richardson told the group, "That money should be spent on our own people."

Earlier Wednesday, Bush told those attending the Veterans of Foreign Wars convention in Kansas City, Mo.: "One unmistakable legacy of Vietnam is that the price of America's withdrawal was paid by millions of innocent citizens whose agonies would add to our vocabulary new terms like 'boat people,' 're-education camps' and 'killing fields.'"

Biden told reporters that the only analogy he sees between Vietnam and Iraq is that Americans in Iraq will be in greater danger the longer that U.S. troops are there.

Richardson issued a statement saying then-President Nixon took seven years to get the last U.S. soldier out of Vietnam after having run on a platform in 1968 to "end the war with honor."

"The correct conclusion to draw from our experience in Vietnam is that dragging out the process of withdrawal will be tragically worse in terms of U.S. lives lost and worse for the Iraqi's themselves in terms of the ultimate instability we will create by staying longer," he said.