I would have guessed that it's an attempt to make other US-friendly countries (Vietnam, Phillipines, India, etc) relatively more attractive as places to set up factories, to move that manufacturing base out of China and reduce their geopolitical influence.
The other--more suspicious and dismissed as conspiratorial--benefactor of of this trade war Russia and the bolstering of Russian industries. America is importing a lot of Russian steel [1] and aluminum [2], and Russia is been ready to fill the food gap for China that they used to get from the US [3].
