Donald Trump mocks Carson's belt-buckle knife attack

Donald Trump attacked Republican rival Ben Carson at a rally in Iowa by questioning his claim he attacked a friend with a knife when a teenager.

Carson had claimed in his autobiography that his friend's life was only saved by this belt buckle, which prevented the knife from wounding him.

Businessman Mr Trump poured scorn on that explanation, calling Mr Carson "pathological".

He also questioned whether Iowans were "stupid" for supporting the retired neurosurgeon in large numbers in the polls.