Donald Trump cuts an erratic figure, but he has his own remorseless logic.
In the form of a looming trade war the world is witnessing his refusal to be budged on core beliefs of his 'America First' doctrine.
Forget the Twitter spats and feuds: the President's move to slap punitive tariffs on steel and aluminium imports to the US (10% on aluminium, a mighty 25% on steel) - is intended to showcase Trump-ism in action.
His supporters see it as making good on his promise to focus on American interests - and it fulfils his campaign-trail promise to deal with resentments that American workers have been short-changed by free trade.
In particular, he is targeting heavily-subsidised Chinese imports, which he says have destroyed American jobs in the industrial heartlands.
In starting a trade war, the world is witnessing his refusal to be budged on core beliefs of his 'America First' doctrine, says Anne McElvoy, Senior Editor at The Economist
Trump does has a point about the growing impact of China on the US economy - and that of the rest of the world too.
China now poses as a champion of free trade, while routinely flouting many of the rules and operating a protectionism of its own. It imposes tariffs of around 10 per cent on foreign goods - far more than America or Europe.
They operate sanctions, like the denial of oil sales to North Korea. President Xi embraces globalisation in speeches - but both formal and informal restrictions make it hard for western companies to thrive in the Chinese economy.
As China grows more mighty and its economy (particularly in technology) gets more sophisticated, competition with the US and indeed the rest of the world, is becoming more intense in sensitive areas. This is particularly true in the collection of personal data to enhance Artificial Intelligence (AI) and military-industrial technology. The President is not alone in worriying about Chinese robotics and AI companies using access to American firms and university research to steal intellectual property in the innovation race.
If Russia now occupies the role of disruptive irritant, with crude attempts to sway election races and a cat's paw approach to testing the West's security mettle in Ukraine, Crimea and by support for anti-democratic forces in eastern Europe, it has receded as an economic and commercial threat.
The stark reason is that the Chinese have advanced far faster in technology in recent years - and that Beijing is keen to weaponise these advances in an intense race with the West for prosperity and economic power.
So the latest set-to on tariffs is part of a much wider potential conflict, which could involve the whole world. Merely hitting back by imposing American duties will not solve the problem. Trade between the US and China needs to come into better balance. But that will be a hard accommodation to reach, as both sides dig in on their national interest in a trade war that is about more than just steel and peanut butter.
Meanwhile Trump's neighbour Canada and the EU are the territories which export the most steel to the US – so the impact is already felt far beyond the US-China stand off. The move has even united fractious Europeans in condemnation. Emmanuel Macron, the EU leader who recently