How Europe left itself open to terrorism
French Police (AFP Photo/Lionel Bonaventure)

This story was co-published with PBS Frontline. In June of 2015, a Belgian ex-convict named Mohamed Abrini flew to Turkey, slipped across the border into Syria and reached the Islamic State’s capital in Raqqah, where he met up with a boyhood friend planning a devastating terror strike on Paris. Watch the Film “Terror in Europe” premieres…