Trump’s controversial remarks about NATO, questioning member contributions and even suggesting the U.S. might not uphold its defense commitments, as well as the decision to halt the deliveries of weapons as well as the sharing of intelligence with Ukraine following the meeting with Zelensky at the White House, have raised alarms across Europe.
Once this kill switch stuff keeps popping up:
https://theaviationist.com/2025/03/10/f-35-kill-switch-myth/
TL;DR: There is no kill switch per se (as in flip it and brick the thing), but a huge dependency on logistics, services and systems that operators outside the US have no influence over. That in turn will cause the plane - while still flyable - to be grounded over time as it cannot be maintained, rearmed and operated effectively anymore.
At the end the effects are the same of a kill switch