The US has done this historically for allies, too, a small deployment along with a public reiteration of a defense commitment isn't saying the troops are intended to be sufficient to resist a threat, it is intended to show that going from threat to war means war with not just the territory attacked, but the power deploying (even small) forces, and potentially all of their available capabilities.

This is especially the case when the tripwire force is deployed by a nuclear power on the territory of a non-nuclear power facing a conventional threat from a nuclear power.