It’s 1:30 a.m., a time when most people are asleep.Your neighborhood is in darkness, except for a few street lamps. Someone—he doesn’t identify himself and the voice isn’t familiar—is pounding on your front door, demanding that you open up. Your heart begins racing....

There was high drama last week when Rep. Devin Nunes announced at the White House that he had seen evidence that the communications of the Donald Trump campaign people, and perhaps even Trump himself, had been “incidentally collected” by the US government. If true,...