Donald Trump has been warning that the US policy of admitting refugees from certain regions - the Middle East or, more generally, Muslim nations - presents a serious threat to US national security. He has attempted to bolster his case by citing often debunked internet rumours, such as that Syrian refugees are largely young, single men. He has called for the US to suspend resettling refugees until "extreme vetting" procedures can be implemented, including ideological tests to screen out extremists. He asserts that nations in the Middle East - which have already received millions of Syrian and Iraqi refugees - must do more to create safe zones for those fleeing the violence.