Suppose President Donald Trump's foreign policy is random. I mean really random: Like random luck, designed only in so far as to fluctuate wildly between different, opposing strategic views.

In this thought experiment, it's not a bug but a feature that the United States is pulling away from a nuclear non-proliferation agreement with Iran even as it seeks to negotiate one with North Korea. Similarly, it's an intentional accident that Mr Trump is replacing the realist national security adviser H.R. McMaster with the conservative idealist John Bolton.