He is incapable of doing anything else. And he needed the stocks to drop so he, his family and billionaire friends could go on a buying spree. In a couple of weeks he will back off, the stock market will go back up and they’ll make millions of dollars. You can be sure, anything Trump does is for his and the family’s financial gain.

The USA, in common with most of the world, is weaker economically than China, because for decades the "advanced" countries farmed out manufacturing to countries with cheaper labour and wore blinkers when it came to realising that China was insiduously building a near monopoly in manufacturing. Now, having destroyed their "home based" industries, it would take a decade at least to get them back to any sort of presence.
If Trump wants tarrifs, they should be imposed on items like Apple products manufactured outside the USA. But, of course, that would hurt his personal wealth and power, so Apple products are exempt. That is just one example, of course. Many big American businesses make their products abroad. Apple is merely the biggest financially.

HMIM, and anybody who believes he has anybody's best interests at heart except his own deserves whatever they get......