And if they do?
Or, they MAY decide to build their own capabilities which are substantial. And we gradually wind down.
If they won't pay then why would the wind down be gradual? I would think it'd be pretty immediate.
They will pay until/unless they replace.
If the U.S. shows itself to be an unreliable ally, and bought allies are by definition unreliable, then they have no choice but to look elsewhere.
“And if they do?”
The US should abandon every nation that refuses to carry a fair burden.
Saved monies should be invested in Fortress America.