The reason that Islamist militants can assert that jihad is necessary against the perceived enemies of Islam is that there is sufficient ammunition in the Quran to buttress their beliefs. The same could also, of course, be said for the Old Testament, which is full of scenes of violent death visited on the enemies of God.

Every lethal terrorist attack in the United States since 9/11 has been carried out by an American citizen or a legal permanent resident, not by recent immigrants or by refugees. So tamping down immigration won't fix the real issue, which is 'homegrown' terrorism.