The series of economic and financial developments on Friday was a strange, bewildering, exhausting microcosm of why the global economy is at risk of a meltdown.

It showed the odd interplay at work between the Chinese government’s actions in the escalating trade war with the United States, the sober-minded global central bankers who have limited power to deploy and an American president whose public pronouncements often appear driven by grievance more than strategy.

President Trump arrived in France on Saturday for a meeting of the Group of 7 industrialized nations, having set the stage for fireworks and confusion. In one dizzying day, he had seemed to be searching for whom or what to blame for economic troubles, first using Twitter to call his own Federal Reserve chief an enemy of the United States and then to urge American companies to stop doing business with China.

And that was just while the markets were open. Later Friday, he said he would apply tariffs to all Chinese imports and increase those already in place.