Forget the towering slabs of steel and concrete sprawling across the southern border. Quietly, beneath the tangible symbols of Donald Trump’s immigration clampdown, another revolution has taken hold. A revolution of invisible digital watchtowers, wires and algorithms – that is as impressive as it is unsettling.

The curtain shielding this vast expansion of America’s digital surveillance technology has, thanks to recent disclosures, been drawn back to reveal at its core a controversial and critically influential digital engine churning through data.