Demonstrators blocked a highway in Arizona as Donald Trump prepared to stage a rally near Phoenix. <br /> <br />The front-runner in the race to be the Republicans' US presidential candidate addressed supporters in Fountain Hills. <br /> <br />Some 50 protesters caused traffic jams as they held up posters with slogans such as "Dump Trump". <br /> <br />The billionaire's rallies have been marred by a series of recent incidents. A meeting in Chicago a week ago was cancelled after protests. <br /> <br />Hundreds of demonstrators had gathered at the University of Illinois and fighting broke out between supporters and protesters in the auditorium where Mr Trump was due to speak.
