Sorry but there is no law or anything that says he has to prove what he says.  He stated an opinion and if you have facts to the contrary then let us see them. If you don't have any facts you are just as full of hot air as Trump.  There is no libel here, this has nothing to do with libel.  Libel needs to be against an identifiable legal entity or group.  Illegal aliens are neither so you can say whatever you like about them with no fear of legal repercussions.  Sorry to tell you but thousands of politicians state their opinions daily with no facts presented.