Let the witch hunt begin. Are you now or have you ever been an illegal immigrant?

Are any of your friends illegal? Relatives?

The last place you’d expect to encounter a chilling moment is at a presidential debate sponsored by National Public Radio. But on Tuesday, there was the NPR moderator, Steve Inskeep, asking the Democratic candidates whether American citizens have an obligation to turn in people they suspect are illegal immigrants.

It was not just a question asked in passing. Mr. Inskeep pressed the issue. He asked Senator Chris Dodd, for example, about the hypothetical situation of a “citizen” interviewing for a nanny.

“You interview a number of applicants,” Mr. Inskeep said. “They all seem very nice. They seem like they would take care of the kids. But it would appear that their documents may not be in order. What would you want an American to do?”