What did Donald Trump do today?

He admitted the "deal" with China on ending the trade war didn't exist.

Trump continues to insist—and, given his grasp of economics, may even believe—that the United States can "win" a trade war with China. Yesterday, he bragged that his "highly successful meeting" at the G20 summit with Chinese President Xi Jinping was the basis of "an incredible deal," one that would be "one of the largest deals ever made."

In reality, all that was actually agreed to in the brief Xi-Trump meeting was for the United States and China to delay the latest rounds of threatened tariffs for 90 days.

This morning, Trump, who is now backed into a political corner by his own trade policy, began the process of lowering expectations in a four-tweet sequence [emphasis added]: 

The negotiations with China have already started. Unless extended, they will end 90 days from the date of our wonderful and very warm dinner with President Xi in Argentina. Bob Lighthizer will be working closely with Steve Mnuchin, Larry Kudlow, Wilbur Ross and Peter Navarro...........on seeing whether or not a REAL deal with China is actually possible. If it is, we will get it done. China is supposed to start buying Agricultural product and more immediately. President Xi and I want this deal to happen, and it probably will. But if not remember,..........I am a Tariff Man. When people or countries come in to raid the great wealth of our Nation, I want them to pay for the privilege of doing so. It will always be the best way to max out our economic power. We are right now taking in $billions in Tariffs.* MAKE AMERICA RICH AGAIN.....But if a fair deal is able to be made with China, one that does all of the many things we know must be finally done, I will happily sign. Let the negotiations begin. MAKE AMERICA GREAT AGAIN!

All three major American stock indices dropped 3% or more on the news. 

* Trump appears to genuinely believe that tariffs are paid by foreign companies directly into the treasury of the United States. In reality, they are taxes paid by American importers, who then pass the costs onto American consumers in the form of higher prices.

Why is this a bad thing?

• It's really, really important that the President of the United States either know something about economics or be willing to listen to those who do.

• The economic health of the United States is more important than Donald Trump's need to save face.