Presumptive Republican presidential nominee Donald Trump speaks at a rally on June 18 in Phoenix. (Ross D. Franklin/Associated Press)

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“PROFILING IS something that we’re going to have to start thinking about as a country,” Donald Trump said Sunday on “Face the Nation” when CBS’s John Dickerson asked him about increasing the use of profiling of Muslims in the United States. “I have seen it recently,” he explained. “We had tremendous numbers of people coming into a speech I was making. And people that obviously had no guns, had no weapons, had no anything, and they were being — they were going through screening. And they were going through the same — the same scrutiny, the absolute same scrutiny as somebody else that looked like it could have been a possible person.”

How was the NRA-endorsed Mr. Trump so sure that so many of those attending his rally “obviously had no guns”? And what, exactly, does a “possible person” “look like”? Brown? Male? Bearded? Wearing a thawb?

Mr. Trump’s thinking is not just poisonous in a pluralistic society, but also pointlessly and counterproductively so. Nearly everyone who might look like a threat to Mr. Trump is not a threat, and security experts warn about wasting time scrutinizing stereotypes rather than focusing on other risk factors. Mathematicians have concluded that profiling’s efficacy is so limited that randomly selecting people for scrutiny may be the better policy. It isn’t possible to build a highly accurate profile of a potential evildoer, and profiling can easily lead to wasting resources checking and rechecking the same innocent people over and over again.

Like so many of Mr. Trump’s policy programs, subjecting Muslim Americans (if that’s who he has in mind) to increased, special scrutiny would also counterproductively stigmatize, isolate and alienate a largely peaceful and patriotic minority group. Muslim Americans would be less likely to cooperate with authorities, which is essential for fighting extremism in their communities. Meantime, real terrorists would figure out how to avoid matching the profile.

Mr. Trump said Sunday that other countries, such as Israel, profile, because it is “common sense.” But the Israeli airline screening system, for one, relies heavily on behavioral observation by trained agents. The Transportation Security Administration’s behavioral detection officers perform a similar role, if less intensely. We doubt Mr. Trump’s untrained eye was looking for the same cues the experts do as he scrutinized his rally attendees. In fact, Mr. Trump’s comments suggest yet again that his worldview is rarely, if ever, more than skin-deep.

Mr. Trump fails to grasp a crucial fact about the United States: This country is based on the notion that people have inherent dignity that derives from their individuality, the unique combination of talents, character and actions that define their quality as human beings. We have a free society so that individuals may make the most out of their gifts, rather than see those qualities ignored or wasted because of superficial prejudice. Practically every day, Mr. Trump proposes to betray this principle in some way. Sunday, in that sense, was just another day.