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President Trump will rally supporters in El Paso Monday evening, where he is expected to use the city as part of his case for building more walls along America's southern border.

"The border city of El Paso, Texas, used to have extremely high rates of violent crime — one of the highest in the country, and [was] considered one of our nation's most dangerous cities," Trump claimed in his State of the Union address last week. "Now, with a powerful barrier in place, El Paso is one of our safest cities. Simply put, walls work, and walls save lives."

This may be a compelling argument, but the facts don't support it. As is the case across the country, violent crime has markedly declined in El Paso for decades after peaking in the early 1990s. It was already historically low when Congress approved new border wall construction in 2006 and when new barriers were built in El Paso in 2008 and 2009. In fact, NBC reports, violent crime in the city actually increased during and after those years of wall construction.

Speaking on CNN Saturday evening, El Paso Mayor Dee Margo (R) said Trump must have been given "misinformation" for his SOTU claim about El Paso's past crime rates, because it was "not factually correct." Should Trump repeat his claim at the rally, Margo said, he would "absolutely" correct him.