For months, Republican presidential hopeful Donald Trump has been promoting a very specific and outlandish strategy to prevent illegal immigrants from entering the U.S. As president, he says often, he'd simply build a wall along the entire Mexican-American border. It'd be funded by the Mexican government, Trump claims. Former Mexican President Felipe Calderón doesn't think his country would be down with that plan, CNBC reports. "Mexican people, we are not going to pay any single cent for such a stupid wall," he said.