I stepped up to the counter at Ben Gurion Airport and handed the young woman my Swedish passport. She eyed me up and down as she typed on her computer. I had taken that same flight, Stockholm to Tel Aviv, dozens of times, but this day was different. The clerk kept my passport and told me to take a seat in a room at the back of the hall.

Two hours later, a member of the Israeli security service interviewed me. She asked about my travel patterns, my family history, my professional and political affiliations. She even asked to...