In advocating for border security, President Donald Trump has repeatedly sought to enlist Border Patrol agents and their union, the Washington Post reports, even bringing union leaders for Border Patrol and Immigration and Customs Enforcement to the White House “to tout the wall.”

That isn’t surprising in one sense: Lots of politicians use uniformed law-enforcement officers as political props. But in another sense, it is rather strange. Typically, unions zealously oppose anything that makes the labor of their members less necessary. The Luddites smashed automated looms. The grocery-store checkers are against self-checkout kiosks. The fast-food workers don’t want touch-screen ordering.

Why would union officials representing men and women who patrol the border be in favor of a barrier intended to stop migration better than humans?

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The most charitable explanation is that members of the union earnestly believe that Trump’s desired wall is in the best interest of the United States, regardless of its effect on their personal interests as laborers. That’s the impression Trump wants to create by touting their endorsement: that the men and women actually patrolling the border, with all the attendant expertise their daily work confers, believe that the sort of barrier he’s advocating for will help them achieve their mission.