You tell a foe by his or her actions.

you tell the foe by his acts in the past and his desire and ability to do the same in the future ...simple....look at the majority of terrorist attacks in the last 20 years who did them? If these attacks continue sooner or later America will get enraged and when that happens; think Germany or Japan in 1945. We are not nice people at that stage sir. I prefer that this be prevented BEFORE it reaches that tipping point . Which means find a means of knowing who we let in before we let thousands in. The WW ll generation  had to deal with the Germans and Japanese..We had to deal with the Commies and the Islamic terrorists will be the major problem of this generation  You know my solution ,if you or your generation can find a better one..good luck to you. I have studied the history of Islam and the Koran and see much good in it, I hope your generation can find a solution to the problem before they annoy us and the Russians and the EU to the point that we go mongol on them.