Have you even looked at illegal border crossings versus the current "wall"?
From about 2006-2010 we built 700 miles of "wall" (much of it is only cattle fence or vehicle blockades, but a portion of it, about half, is "real wall") and illegal border crossings fell from about 1.2 Million per year to about 400,000 per year. While some of those 400k go under or over the "wall", the vast majority go around the wall or through the large gaps. Coyote trails are littered with trash where these crossings occur. It's pretty compelling that incrementally increasing the "wall" would incrementally reduce illegal Southern border crossings, especially by plugging the currently popular "gaps".
Interior enforcement also affects illegal immigration... since Trump's election, it is obvious that enforcing the laws by finding and deporting illegals reduces the number who come in the first place. If the odds of getting here AND STAYING are reduced, fewer are willing to try to begin with.
Visa overstays are another, but separate problem. The biggest issue is that no one can say how many people, and who, have entered on Visas and remained after their Visa expired. (thanks Obama) This needs to be rectified. But, one positive about Visas is that if you violate immigration laws, you will not be allowed entry on Visa. Border crossers, on the other hand, try again and again and again.
To argue that you must have a plan for an impenetrable "moat" before building or enhancing a single mile of the wall is an intellectually false argument. It indicates that one is just fine with 400,000/year illegal border crossings (or, to the extreme, advocate open borders).
I disagree.
For some reason we had to go through all that other crap just to get to this point. Now we're getting down to brass tacks. No I haven't paid attention nor do I have much detail with regards to how big a problem boarder crossings are. But the fact you have such a poor messenger with such a poorly crafted and simple mind numbing message doesn't help matters one bit.
Now if these numbers are correct it appears that we have reduced the problem significantly already. So maybe such a complete wall might not be necessary. I'd still like to see a bit more along these lines as well as seriously discuss cost. Before someone makes a point that my list of questions will expand after the fact, I retain the right to do that if I think of anything along those lines later. Discussion means discussion.