It’s best to presume that anything done won’t satisfy him, but instead to give him just enough that he can claim some sort of victory and walk away from the entire issue. Just flatter him and tell him that the increased NATO spending is all because of him, despite the fact that in reality is has nothing to do with him or even the US.

Then do what’s best for the rest of NATO, presuming that the US won’t be helping, and may even hinder at inopportune times.