Of course it's not impossible to have a full wall. Look at the peaks and valleys that the Great Wall of China goes through! The mountainous area around El Paso is the only place where it's even dicey, and there, you can use the mountains themselves to do it.
Besides, the "impossible" quibble is being technocratic on a political issue.
It may be very difficult to actually build a sea-to-sea wall, when you get down to certain areas, but it most certainly is not impossible to PROMISE it, and put the principle in legislation, and start erecting it rapidly in all the rest of the areas.
It will take years to complete the whole thing, but in the process of building it we should get a very good idea of where the immigrant flows are moving as the wall are built.
If an immigrant can go through an area, then a wall can be built there. If terrain is so impossible that it's impassible, then it's a natural wall. And we'll see that as the regular wall is built.
There is no cost in agreeing in principle to a sea-to-sea wall, other than the EVENTUAL likelihood that you'll be pressed to complete it.
And truth is, by that point (6 or 7 years down the road) the presence of the wall already built will have done one of two things:
(1) Been very effective at cutting the flow to a trickle, which will make it very easy to persuade everybody who still worries about the border at that point that a "Virtual Fence" is sufficient, or
(2) Have channelled the whole huge flood of illegal immigration into those extremely remote places where it is difficult to build a wall, demonstrating why it is there, especially, above all, that a wall needs to be built.
Either way, the current political crisis will be averted, by letting BorderBots hear precisely what they want to hear (knowing full well that plans are modified in the out years) and keeping Congress.
What's hard about that?
The trouble is that by being excessively technocratic and telling a population that watched us land on the Moon that a wall "can't" be built somewhere in the desert, what BorderBots are hearing is that you don't really WANT to, and that you don't WANT to concede a real physical barrier, preferring a "virtual" barrier which doesn't actually block people...but which, rather, can be enforced or nor enforced based on the political climate of the moment.
That is precisely the opposite of what Border Conservatives want. You've got to bend on this. EVEN IF a wall is technically impossible along every inch of the border (it isn't), you concede the general point of building a wall the whole way, and start doing all the easy parts, and win the election THIS year. Then, 5 years down the road when you come to the El Paso mountains there won't even be a public debate when you "go virtual" because the physical wall is too hard. So long as that little gap of virtual fence does not become the hole in the dyke through which a million illegals pour, nobody is going to have a political hissy fit if the illegal immigration problem has been significantly reduced by the existing wall.
INSISTING on fighting over technical "impossibility" issues with Americans, now, in the heat of battle over the PRINCIPLE of a wall, might be completely sincere but politically flat footed. What it SOUNDS like, though, is the camel trying to stick its nose under the tent to get the PRINCIPLE of a "virtual wall" in place. BorderBots know that a "virtual" wall is a DISCRETIONARY wall, and they will think that you're trying to pretend to give them everything while giving them nothing.
It won't work politically.
Promise them a physical wall. And nobody will even notice in 5 years when you have to gap the really hard sections with a virtual fence, so long as it works. Do not waste political capital against a suspicious and hostile part of your base to try and give them an engineering lesson in the middle of a political battle. You'll just be shooting your own foot off.
I look at it more simply: We can send a man to the moon, we can shrink supercomputers down to microcomputer size, we can tally 50 million votes for American Idol in two hours, but we can't BUILD A WALL? We can't do something the Chinese did thousands of years ago?
I thought the US was an optimistic country! THe can-do spirit is our way, always has been. If we have lost our gumption to where we say it's impossible to build a wall, no matter how inhospitable the terrain, then I daresay that the fall of the US will come soon (and not from illegals), because we've lost the spirit that made us uniquely American.