Barack Obama has been challenged to a debate by former Governor of Iowa, and declared candidate for the Democratic nomination, Tom Vilsack.
Vilsack and the other declared candidates will be taking part in a forum on February 21 in Carson City, Nevada. However, Obama will not be attending, choosing instead to campaign in Iowa.
Vilsack has offered to fly out after the forum in Carson City and meet Obama for a debate in Iowa that night.
Obama's campaign have so far not taken up the offer.