In a battle of endorsements Tuesday, filmmaker Ken Burns called the Clinton campaign too negative, and former NBA superstar Earvin "Magic" Johnson called Barack Obama too inexperienced to be president.

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Burns made his comments while endorsing Barack Obama for president.

The Walpole, N.H., resident said Obama has consistently presented a positive agenda for the country, while politics has descended into "cynical slash-and-burn character attacks."

Burns, who recently produced the documentary "The War," about World War II, as well as "The Civil War" and "Jazz," said he has known the Clintons for 15 years, and that Hillary Clinton will likely "clean up the act."

Johnson, appearing with the Clintons Tuesday in Iowa, said he doesn't trust rookies to win a basketball game, much less lead the nation.

"You don't want somebody in there that is young or a rookie at politics," Johnson said Tuesday at a raucous rally in support of presidential candidate Hillary Rodham Clinton. "We want somebody in there that knows what they're doing because this job is so huge."

Implicit in Johnson's comments was the suggestion that Hillary Clinton had more experience than her rivals Barack Obama, who has served in the U.S. Senate since January 2005, and John Edwards, who spent one term as a senator.

Johnson didn't mention that he won his first championship with the Lakers as a rookie, and was named most valuable player in the NBA finals that year.

The issue over experience also made news Monday when Obama used Bill Clinton's own words to attack the former president's suggestion that Obama didn't have the right resume to run for office.

As a first-time presidential candidate, Clinton cast himself as an "agent of change" in troubled times, and faced criticism from Republicans about his youth and inexperience.

"Here's a quote," Obama said with a smile. "'The same old experience is irrelevant. You can have the right kind of experience or the wrong kind of experience. And mine is rooted in the real lives of real people, and it will bring real results if we have the courage to change."'

"And that was Bill Clinton in 1992."