Donald Trump shook up America. Now it's the world's turn. The President-elect's decision to flout 40 years of diplomatic convention and take a call from Taiwanese President Tsai Ing-wen last week suggested he may be just as disrespectful of protocol on the world stage as at home. The call produced days of speculation about how the President-elect's impulsive style will reverberate around the globe and whether it could threaten the architecture of international relations. There are many global traditions and arrangements that he could target, though each could carry a geopolitical or diplomatic price -- one reason even presidents who...