[BeauBo]

"How does 1,080 miles effectively seal off the whole US-Mexico border?"

Along with the earlier 26 and 150 miles of the earlier phases, the total is about 1,250 miles of strong barrier, out of a 1,950 mile total border.

I assume they mean that the remaining 700 miles is so rugged and remote, that it delays/deters even more than a thirty foot wall. Nothing is impenetrable, but 1,000 or 1,250 miles of strong barrier strategically positioned, manned by a strong Border Patrol equipped with the right equipment and technology, can effectively control the border (no remaining safe or easy routes).

For example, this stretch of the Rio Grande River border in Big Bend, is more challenging than a 30 foot wall:

[OrangeHoof]

Never mind the Bollards. Where are the (***) Pistols?

[deport]

According to our new map, there are 700 miles of fence along the U.S.-Mexico border –
a Customs and Border Protection spokeswoman recently said the total is 702, so our
tally is very close to the agency’s. However, in some high-traffic spots, there are two or
three layers of fence in one place, leaving somewhere between 652 and 690 miles of the
border actually covered by fence.

https://www.revealnews.org/article/the-wall-building-a-continuous-u-s-mexico-barrier-would-be-a-tall-order/

[9YearLurker]

It’s also beautiful—though of course not nearly 700 miles long.