Are you sure it’s that much? Nanzi was pretty flinty with allocations for the wall. I think DOD had paid for most of it.
It seems to me that recouping $2.6 billion might be only from terminating the remaining DoD funded projects. This is the first report with some numbers, but the details are still vague.
Congress put up about 1/3 of the money (4.6 billion), but that money is mostly dedicated to specific miles in the Rio Grande Valley and Laredo Sectors, that have not been built yet, awaiting acquisition of private lands. Even if they allow those contracts to run, it will end up full of holes, if the Administration refuses to use eminent domain to take the land from hold outs.