The accident caused Michelle Obama to cancel her final campaign stop of the day, telling about 40 people who waited more than 75 minutes at a park shelter it wasn't the time to stump for her husband, the Illinois senator who is seeking the Democratic nomination for president, The Washington Post reported. "We're a little shaken, but fortunately it could have been a lot worse," she said.

The helmet-less motorcyclist, Tim Emerson, 40, of Iowa Falls, suffered a cut on his head. Another motorcyclist told the newspaper Emerson pulled out to pass two vehicles on Highway 65 near Hampton and hit the driver's side of the campaign van as a staff member made a left-hand turn.

"He got in a little bit of a hurry and tried to go around everybody," said Mark Keller, a friend of Emerson's. "He went around two other cars that he shouldn't have."

Obama Iowa campaign spokesman Tommy Vie said "our only worry" was that Emerson would be all right.