Surely the tariff/trade debate. The question is which side pulled this particular trigger? Yes, it could be Trump. But it could also be Xi, seeing that Trump just got cold feet vs. Mexico and thinking he could get ahead of things and force a concession.

Folks, this is why you don't engage in brinksmanship at this scale. It gets out of hand really quickly. I await the coming economic crisis (I mean, the stock market was already primed for a correction) with resigned exasperation.