aggressive attacks yet in what amounted to an hour and a half long ran in the iowa. >> how stupid are the people of the country to believe this crap? >> reporter: the billionaire gunning for carson. the two are virtually neck and neck in recent polls here. after the retired neurosurgeon wrote in his autobiography that as a teen he tried to stab a friend only to have it stopped by a belt buckle. >> i have a belt. somebody hits me, it's going in. the belt moves this way. it moves this way. it moves that way. he hit the belt buckle. anybody have a knife want to try it on me? believe me, it ain't going to work. >> reporter: trump comparing carson's self-described pathological temper to an incurable disease. >> i don't want a person that's got pathological disease. if you're a child molester, a sick puppy, you're a child molester, there's no cure for that. >> reporter: a theme of attack he used earlier in the night on cnn prompting carly fiorina to