Obviously the "big, beautiful wall" was just a rhetorical gimmick, straight out of the Willie Horton school of political exploitation and demonization. Only barely educated xenophobes would fall for it. And to Trump's credit, he is at least smart enough to know how to exploit xenophobia and racism to his personal benefit.
I have never met a single sentient being who did not think we should have reasonable border security measures, immigration policies, and robust screening measures for those seeking asylum. Nobody wants criminals or people of dubious character being let into the country. But a 2,000 mile long "big, beautiful" Berlin Wall is neither technically or economically feasible, its an optic that is wholly inconsistent with our great reputation as a nation, and it would be an ecological disaster of the first order. Smart people can think up cheaper, and more effective border security measures.