It’s easy to defend against what the terrorists planned last time, but it’s shortsighted. If we spend billions fielding liquid‐analysis machines in airports and the terrorists use solid explosives, we’ve wasted our money. If they target shopping malls, we’ve wasted our money. Focusing on tactics simply forces the terrorists to make a minor modification in their plans. There are too many targets — stadiums, schools, theaters, churches, the long line of densely packed people before airport security — and too many ways to kill people… Last week’s arrests demonstrate how real security doesn’t focus on possible terrorist tactics, but on the terrorists themselves. It’s a victory for intelligence and investigation, and a dramatic demonstration of how investments in these areas pay off.