The deck is always stacked when we debate keeping the nation safe.

Recently, we discovered that the National Security Agency is keeping an enormous file of our phone calls. In the N.S.A.’s defense, its chief, Gen. Keith Alexander, said “dozens” of potential terrorist attacks had been thwarted by that kind of effort. The director of the F.B.I., Robert Mueller, suggested it might prevent “the next Boston.”

How do you argue with that? True, the N.S.A. program had been up and running for years without being able to prevent the first Boston. And Alexander declined to identify the thwarted attacks, arguing that might aid potential terrorists.

But most Americans were sold. The words “terrorist attack” conjured up terrible, vivid pictures. On the other side was just a humongous computer bank full of numbers. If you didn’t do anything wrong, what was the problem?

Today, let’s try putting a face on it in the form of Brandon Mayfield.

A Kansas native, Mayfield went to college and law school, served in the Army, married, had three children and moved to Portland, Ore., to practice law.