 Not least, there's the problem of burden sharing. After a decade of contentious negotiations, Trump's prodding, really, two-thirds of our NATO allies will this year begin to have at least 2% of their GDP spent on their military, as agreed. But one-third won't. America's quasi-allies, those without explicit security guarantees, present another problem. Assuming we have their back, these partners may engage in diplomatic or other kinds of confrontations.