What did Donald Trump do today?

He complained that China was fighting back in the trade war.

American stock markets plummeted today, with major indices losing between 2.9 and 3.5% of their value in a single session. As the carnage unfolded, Trump was on Twitter blaming Chinese currency manipulation for the sudden shock to the economy. He said that the Chinese government had artificially devalued the yuan, and that this was a “major violation.”

The problem is, he’s probably correct—and there’s not much he can do about it.

The abrupt devaluation, to the lowest rate against the dollar in eleven years, is just one form of retaliation that Beijing has at its disposal, now that talks to end the trade war Trump started last March have once again collapsed. It effectively lowers the costs of Chinese-made goods, counteracting the effect of the extra taxes American consumers pay as the result of Trump’s tariffs.

More than 18 months ago, when he first announced tariffs against China, Trump predicted a quick and easy win to the trade war.

On Twitter today, Trump also predicted that the devaluation would hurt China’s economy. In the long run, that might be true—just as Trump’s tariffs have inflicted hardships on American consumers and all but crippled certain key economic sectors. But it is hurting the American economy much more now, precisely when Trump is most vulnerable politically.

Economists from all over the political spectrum, including his own advisors, warned Trump away from the trade war, only to be ignored. Trump didn’t say what plan, if any, he has to respond beyond complaining about the unfairness of it all on Twitter.

Why should I care about this?

• A president who knew even the basics of how the economy works would not have been surprised that this happened.