This Oct. 26, 2017 file photo shows prototypes of border walls in San Diego. Rigorous testing of prototypes of President Donald. A U.S. official says recent testing of prototypes of President Donald Trump's proposed wall with Mexico found their heights should stop border crossers. U.S. tactical teams spent three weeks trying to breach and scale the models in San Diego. An official with direct knowledge of the results said they point to see-through steel barriers topped by concrete as the best design. The official spoke to The Associated Press on condition of anonymity because the information is not authorized for release. (AP Photo/Elliott Spagat, File)
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