I disagree. The US can't turn off all GPS, short of blasting EU, Russian and Chinese satellites out of the sky. I have an affordable GPS module on my desk right now that already detects spoofing with a fairly high degree of reliability.

But GPS is just one thing in the navigation toolbox. There are so many other ways for drones to orient themselves, from triangulating on RF signals to object recognition and location with ML, and both of these are now commodity technologies. And capabilities (and thus options) go up considerably once you start mixing and matching systems rather than leaning heavily into a single design.

When I say commodity technologies, I mean this stuff is so cheap and accessible now that I can see belligerents launching drone swarms simply to get the countermeasure batteries to reveal themselves. To an extent this is already happening in Ukraine; Russian ECM is superior to anything fielded by the Ukrainians (and allegedly, to anything the west has), but Ukrainians are in turn selectively targeting Russian ECM trucks.