A constant in Donald Trump’s electoral pitch was that wealthy allies had for too long relied on America’s willingness to backstop their national security and harvested the long-term economic rewards of keeping their own military effort comparatively modest.
We’ve no real idea at this point where a Trump administration will see the balance of American interests on this issue. We have to be optimistic that the President-elect will recognise that the way he was inclined to frame this question when he was a candidate was simplistic and not especially helpful. Americans won’t want the US to be portrayed as a ‘gun for hire’, a mercenary power that charges what it thinks it will cost to sustain a military posture that will deter and, if necessary, defeat the opponents of an ally; if the ally doesn’t pay their full share, the deal is off.
In fact, the pact between allies is profound and quite remarkable—a willingness to accept that a nation’s most treasured asset, its sovereignty, should depend to some degree on another state and a willingness to risk a state’s most treasured resource, the lives of its citizens, to protect the sovereignty of another state. The considerations that each party brings into play to assess the merits of an alliance relationship are broad and intangible—not the sort of thing that anyone can readily put a dollar value on.