Unwelcome Return

It was no doubt inevitable, but that only made it more depressing. A Palestinian suicide bomber shattered the regions three-month period of calm Friday night by killing four Israelis and injuring 50 outside a crowded Tel Aviv nightclub. The bomber, a 21-year-old student from a village near the West Bank town of Tulkarem, was the first since the November death of Yasser Arafat; he hoped to destroy the tenuous trust that took root at a Feb. 8 peace summit in Egypt.

To keep him from succeeding, Palestinian security forces — which in the last four years...