Then, a few hours later, Mr. Powell gave a speech at the Fed’s annual conference in Wyoming in which he said uncertainty about global trade was weighing on the economy, and the Fed wasn’t entirely sure what to do about it. The remarks amounted to an implicit rebuke of Mr. Trump’s trade policies. While Mr. Powell left open the possibility that the Fed will cut interest rates this fall, he stopped well short of promising anything like the kind of dramatic stimulus campaign Mr. Trump has insistently called on the central bank to deliver.

The double indignity apparently was too much for Mr. Trump to suffer quietly.

“As usual, the Fed did NOTHING!” he began, then called Mr. Powell an enemy.

Mr. Trump has reason for economic anxiety: A growing number of forecasters predict that the longest period of economic growth in American history is drawing to a close.

And a downturn would make it harder for Mr. Trump to win a second term.

But the president’s insistent efforts to preemptively pin the blame on Mr. Powell and the Fed’s management of monetary policy don’t hold up to scrutiny . The Fed raised rates a little too high last year, and there is a reasonable case for lowering rates this year. But the biggest worry for the American economy right now is that corporations are sitting on their wallets, in part because of uncertainty about the impact of Mr. Trump’s campaign to disrupt existing patterns of global trade — especially between the United States and China.

Stanley Fischer, a former Fed vice chairman, said Friday in Wyoming that Mr. Trump is “Trying to destroy the global trading system.” Anxiety about global trade, and about Mr. Trump’s disruptive approach to international relations, is likely to feature in the discussions among leaders of the G7 nations when they gather in France this weekend.

There is also an important difference between questioning Mr. Powell’s judgment and calling him an “enemy.” Mr. Powell is a public servant who was nominated as Fed chairman by Mr. Trump and confirmed by the Senate, and who has conducted himself with admirable dignity in the face of Mr. Trump’s ad hominem attacks. His judgments as Fed chairman are deservedly subject to scrutiny and debate. But the unfounded accusation that Mr. Powell is an enemy of the United States raises questions about Mr. Trump, not Mr. Powell.

Mr. Trump’s latest moves in his trade war with China are also a cause for alarm.

Mr. Trump used to promise that it would be easy to improve the status quo: He would impose tariffs, and China would quickly agree to make changes like opening markets to American goods, curtailing its subsidies for Chinese manufacturers and preventing theft of intellectual property.