When Donald Trump announced his campaign for the presidency, it came with one central promise upon which the rest of his political agenda would be built: “I will build a great, great wall on our southern border, and I’ll have Mexico pay for that wall.”

Trump’s concerns about the border were reasonable, but his proposal was patently absurd. If former Trump employee Sam Nunberg’s recollections are correct, the wall was dreamed up by the campaign as a “a mnemonic device of sorts, a way to make sure their candidate … would remember to talk about getting tough on immigration.” Building a 2,000-mile concrete wall along the varied terrain of our southern border was impractical enough. The notion that Trump could additionally strong-arm the Mexican government into paying for it was downright impossible.