Story highlights Trump says 11 million undocumented can be expelled humanely

A professor who studied past deportations says it's cruel and deadly

(CNN) Donald Trump is pointing to a 1950s-era federal program as a possible model for his plan to deport 11 million undocumented immigrants, insisting it can be done "humanely."

But one expert who has studied "Operation Wetback" said the program of then-President Dwight Eisenhower was deadly and cruel.

"It was not humane, it was a military style of operation," said Mae Ngai, a professor of history at Columbia University. "[Eisenhower] sent hundreds of border patrol officers to sweep up people."

"In many cases," she added, "they basically herded people on to big trucks and dropped them off on the other side of the border."

Trump has said this week that he would use a "deportation force" to carry out his plan and told reporters it would be done in a "humane" way, but he hasn't provided details. The real estate mogul said he has heard different things about how "Operation Wetback" worked. "I've heard good reports, I've heard bad reports," he told Fox host Bill O'Reilly on Wednesday night.

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