They are not just on the way, they are already here. There have been several attempts to access military bases by foreign nationals, most of which are not on the national news. Check out Angry Cop on You Tube. He had a video about some of them last week
There have been quite a few chinese national males of military age already stopped, then released by BP. Same goes for a disturbingly large number of folks on terror watch lists.
IMO it is not a question of if, it's merely a question of when and how many are going to be activated.