This idea of building a wall has already served its purpose: It helped Trump get elected. As ludicrous as it is to build this monument to abject waste, so too is the idea that "Mexico is going to pay for it" in the way that Trump wanted it to mean to those fools who so dearly wanted to take a bite out of that ridiculously lucious piece of putrid red meat.
Trump appealed to the raw emotions of those he targeted and then he purposely rubbed raw those emotions with such unbeleivable inflammatory flair such that the only folks who believed those lies of his were those that wanted to hear it being said. It didn't matter to them at all that building a wall and having Mexico pay for it was pure unadulterated bullshit. It appealed to the emotions of those that Trump was wooing and that is all that mattered at the time.
Trump simply targeted emotions as his way to victory and it worked.
As we have all witnessed since then, Trump has either gone back on almost all of those promises he's made to the working class and poor folks that voted for him based on those lies of his or he's outright dismissed them as "campaign rhetoric" that shouldn't be taken at his word. To add insult to injury, he's now filling his cabinet with those very swamp critters he said he was going to drain our government from. And from what I've been gleaning from the news, Mitch McConnell has already said all of Trump's choices will be approved so there's no disputing it from that angle.
Let's put to rest this idea that Trump really meant what he said and now actually means what he said about the wall, when all he's doing now is attempting to find a way to get out from under that "promise" of his and is wanting to make it happen in a way that is the cheapest and most importantly, the least damaging to that precious "image" of himself that he's created in the minds of his followers.