Donald Trump has long promised that his “powerful” border wall is necessary to keep out the undocumented immigrants he loves to demonize. But the thing about walls is, they’re not particularly effective if they can be blown down by the wind, or sawed through by smugglers—or, as the Washington Post reported Thursday, if the potential for flash flooding means they must include massive gates that will necessarily be left open for months on end.

Per the Post, monsoon season, which swells desert rivers and tributaries, is a massive logistical challenge for Trump’s wall, which “effectively acts as a sewer grate that traps debris” thanks to his chosen design of large steel bollards spaced inches apart. As water comes rushing through, carrying things like plant matter and tree trunks, the wall “cannot withstand the power of the runoff.” To keep flash floods from knocking Trump’s “big, beautiful” wall over, hundreds of storm gates will need to be installed and left open for months at a time during the summer. Some locations along the border already have such open gates, which have reportedly “allowed for the easy entry of smugglers and migrants into the United States.” Like the myriad other drawbacks to Trump’s thousands of miles of wall, experts more or less saw this one coming. “The border is so diverse,” Roy Villareal, chief of the Border Patrol’s Tucson sector, told the Post. “You have to plan for water flow.”

Villareal and others defended the administration’s wall planning and downplayed the challenges posed by literally opening the doors to the very people Trump maintains must be kept out. But the flooding issue is the latest indication that Trump maybe didn’t think this whole thing through, and that his wall doesn’t exactly make America the impenetrable fortress he promised his supporters it would. That fact was perfectly underscored this week, when high winds toppled newly-installed portions of the wall, which fell onto the Mexican side of the border. At least Mexico is paying for it—right?

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