National security expert flattens Trump's wall argument: 'If you build a 50-foot wall you'll find a tunnel'

A former Justice Department and Homeland Security official trashed Donald Trump for insisting a border wall will result in fewer drugs coming into the United States amid a CNN report on tunnels used to smuggle drugs between Mexico and America.

Early Wednesday morning, the president tweeted that a wall will "put an end to stoppable crime and drugs" — but as CNN noted in its special report, cartels have always and will continue to find ways around barriers at the border.

"In just the past month alone," host Erin Burnett said, "three new tunnels have been discovered in one border town."

After airing a report on the tunnels found in Nogales, Mexico, Burnett brought on Juliette Kayyem, a former high-ranking Homeland Security official and onetime overseer of Border Patrol.

Kayyem noted that Nogales is home to partial border walls that already exist.

The United States' "border enforcement policies have almost no relation to the magnet that draws people and drugs and other things, I think, to the United States," the former DHS official said.

She then quoted former DHS secretary and recently-ousted White House chief of staff John Kelly: "The problem with our border and illegal activity coming across it starts 3,000 miles south of here."

The images from the Nogales prove, Kayyem said, "that if you build a 50-foot wall you'll find a tunnel."

Watch below: