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President Donald Trump assured that the U.S.-Mexico border wall will be built at a swearing-in ceremony for new DHS Secretary Kirstjen Nielsen.

"If we don't get the wall, you're gonna have a lot of very unhappy people, starting with me," Trump said. "We're gonna get the wall."

He said the wall is necessary to stop the flow of illegal immigrants and drugs pouring into the U.S.

Trump reiterated his calls for a merit-based immigration system, in order to attract the best and brightest to come to the U.S. legally.

He also called for an end to chain migration and enhanced border security.

Trump noted that illegal border crossings were at a 45-year low in the 2017 fiscal year, and he said he's confident that Nielsen will "take it to new levels."

"I have absolutely no doubt you are going to be so outstanding, and I want to congratulate you," Trump said.

According to the San Diego Union-Tribune, officials in California have begun testing border wall prototypes to see how easily someone could climb over the top or dig a hole underneath.

Watch the clip above.

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