Historically, there's only one "keep out the invaders" wall that proved effective. Well, actually, let's say "reasonably effective." The Chinese knew that you can't really build walls in some places; it's just not feasible from an engineering perspective. So, the Great Wall is really a collection of walls. There are several gaps, by design (and some not by design, courtesy of lazy/stupid people). On top of that, the protection provided by these fortifications had its limitations. Sometimes, a determined enemy would figure out a workaround, like "build some ladders." Sometimes, a traitorous general would open the gates and let the bad guys through.
The point is that it was clear to many, many people that Donald Trump's proposed border wall was a fiasco in the making. Historians knew that these things rarely work (unless you've got a couple thousand years to work on it). Engineers knew that the border land amenable to wall-building already had fencing on it, and that for the rest, construction was somewhere from "really, really tough" to "impossible." Environmentalists knew that the fence/wall raised all sort of potential problems in terms of impacts on both plant and animal species. Lawyers knew that gaining the legal right to build would be a huge problem because Texans most certainly do not like the idea of the Big Bad Gubmint taking their land using eminent domain, even if they get the fair market value (which is close to zero in most cases).
In the end, the Trump administration only built a fraction of the "wall" that was promised as part of the Trump campaign. It was about 400 miles' worth, was flimsy fencing rather than a wall, and was paid for by the U.S. and not by Mexico. And guess what? Even in its limited form, it's been a fiasco. Given all the carping that Republican politicians have done about "immigration out of control," it is clear that the wall did not solve the problem it was supposed to solve. Beyond that, however, a new and damning report from the Government Accountability Office reveals that the wall/fence was actively harmful to the natural environment.
As president, Trump never had any patience for dotting i's and crossing t's. He also knew that getting something built was essential to his reelection bid. So, he rushed the job, setting aside things like legally required impact studies. And, per GAO, this has had exactly the consequences you would expect. Plants and animals, including some very endangered specimens, have died. Migration patterns have been disrupted. Flooding incidents have been made worse. Much or all of the Trump fencing will have to be removed, and then there will be mitigation costs on top of that. All of this is a shame, but there is at least some schadenfreude in "I told you so." (Z)