Supporters of Donald Trump, the presumptive U.S. Republican presidential nominee, see refugees arriving from Iraq and Syria as one of the greatest threats to the United States, according to a study released on Thursday by the Pew Research Center.Eighty-five percent of respondents who said they supported Trump saw the refugees fleeing the Islamic State militant group as a threat, compared with 74 percent of Republicans overall, said the study.Only 40 percent of Democrats viewed the refugees from the region as a major threat.Trump's campaign said in a statement last December that he was "calling for a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on."