Trump admits Trump Wall will be "see through", not an actual wall
"The wall is happening. In fact, you probably saw, you know, we have a wall up there now, and re-renovating it already. It's being made pristine, perfect, just as good as new, though we may go a little higher than that, but that's OK. And we are building samples of a new wall. You know, it has to be a see-through wall... If you can't [see] through it, you don't know who's on the other side. Let's say we build a pre-cast concrete wall and now we have people on the other side... It's going to stop drugs. It's going to stop a lot of bad things."
Trump promised a solid concrete wall - an actual, physical wall - spanning the entire border. Trump's original Executive Order from January 2017 defined the "wall" to include fencing. Trump fans rejected a truthful reading of Trump's Executive Order and have always thought he'd deliver a concrete wall. To them, it was never fencing, bollards, or a metaphor.
Now, as Trump himself admits it was all just a scam, his fans will do anything to avoid admitting they got scammed. They'll continue what they've always done: expend endless energy spinning for their idol but choose not to make their infallible idol better. Even as he's admitting Trump Wall won't be an actual wall to their faces, they'll pretend they thought it was all just a metaphor all along.
That's not at all to say a wall is needed. Whatever Trump ends up building can be easily torn down by the next President (or even the next Congress). A wall is an easily ripped off bandaid. What's really needed is to make smart arguments that undercut those like Nancy Pelosi to her base. Trump lacks the ability and patriotism to make them, and lacks the will to show his ally wrong.
UPDATE: Another quote from the same speech :
"You don't need it all the way... We are going to have as much wall as we need. ...You have a lot of natural barriers, et cetera. Somebody said, 'Well, what are you going to do, you going to build that wall in the middle of the river? ... That nobody can go in? Are you going to build that wall on the mountain?' I said, 'You don't need the wall on the mountain. You have a mountain which is a wall.' But we are going to build a wall. It is coming along great,"
 thehill · com/homenews/administration/352016-trump-southern-border-wall-is-going-to-be-see-through
 localmemphis · com/news/politics/you-dont-need-it-all-the-way-and-other-things-trump-said-about-the-wall-on-friday/816948721