Fox News host Bill O'Reilly challenged Donald Trump about the presidential candidate's hardline immigration stance on Wednesday night.

Trump has promised to deport every undocumented immigrant and build a massive wall along the U.S.-Mexico border. O'Reilly pointed out that the Eisenhower-era program Trump cited during the debate as proof that his plan would work was extremely flawed.

The controversial policy, known as "Operation Wetback, " sent at least 1 million people -- including U.S. citizens -- to Mexico in deplorable ways.

"That was brutal what they did to those people to kick them back," O'Reilly said. "The stuff they did was really brutal, it could never happen today."

"We would do it in a very humane way," Trump said.

"I back you on the wall," O'Reilly said. "But I also don't think you could deport these people because the federal courts would stop you... each person has to have due process... you know that!"

O'Reilly has challenged the former reality TV star on his immigration plan before, but that criticism continues to fall on deaf ears.

Watch the full Trump interview in the video above. The immigration exchange begins at 5:07.

(h/t Mediaite)