Before enplaning for the G20 meeting at Argentina, President Trump gave an eye-opening interview to the Wall Street Journal. The focus was trade, tariffs, and Communist China. Toward the end, the Journal’s reporter, Bob Davis, asked Mr. Trump about the Federal Reserve chairman, Jay Powell. Responded Mr. Trump: “I think the Fed right now is a much bigger problem than China.”

What a remarkable thing for the — or any — President to say enroute to a sit-down dinner with the Chinese party boss (Messrs. Trump and Xi seem set to sup Saturday), and we, for one, were delighted to hear the president make the point. It’s not that the Sun is dug in one way or another on interest rates, even if Mr. Trump is irked at the Fed chairman for raising them. It’s that it opens up the monetary debate.

It would be a lot easier for the world financial leaders gathering in Buenos Aires to figure out coherent policies were an honest monetary system functioning today. Instead, the world has been at sea — a sea of fiat money — since the collapse of the Bretton Woods system in 1971. It’s a tragedy that Mr. Trump and the 115th Congress failed to step to the problem when the GOP had control of the House.

Particularly because, during the campaign, Mr. Trump seemed to grasp the problem. The issue erupted at the GOP debate at Boulder, where Rick Santelli of CNBC put the question of the Federal Reserve to Senator Cruz. The Texan nailed it, replying that the Fed should “get out of the business of trying to juice our economy and simply be focused on sound money and monetary stability, ideally tied to gold.”

During the campaign, Mr. Trump went on to signal an appreciation for the monetary problem. He complained about Communist China’s manipulation of its currency. Plus, the GOP platform addressed monetary reform. It endorsed Audit the Fed, a measure to give Congress, to which the Constitution grants the monetary powers, greater oversight of the central bank it created.

The GOP platform also endorsed the creation by Congress of a commission to reconsider monetary reform. That measure, and Audit the Fed, had already passed the House and were, when the platform was written, stalled in the saucer of the Senate. These columns urged Mr. Trump to get on top of the issue before the moment passed. With the accession of the Democrats, the moment is . . .

. . . lost, we’re tempted to say, but we’re not so sure. Audit the Fed once passed the House by a vote of 333 to 92. No doubt there is an enormous investment by the government in inflation. The government debt held by the public is on the order of $16 trillion in irredeemable electronic paper ticket money. How the government would like to pay back its creditors with money worth less than the money it borrowed.

There are, though, countervailing issues. Mr. Trump ran for office criticizing the Federal Reserve, warning that the regime of quantitative easing and ultra low interest rates had created under President Obama a “false economy.” He’s in danger of contradicting himself in his warnings about the Fed’s recent itch to bring up interest rates. Does he want to be accused of plumping for a false economy?

In any event, better to have a standard set in law to which everyone can refer — a row these columns have hoed many times. This is the first time, though, that we’ve had a President of America going into a global summit talking about how Red China is not as big a problem as the Federal Reserve. Put into plain English that means that Mr. Trump comprehends unintended consequences of fiat money. If he really wants to take on a Fed that is a problem bigger than China, he’ll start redeeming the promise of monetary reform.

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Correction: Boulder was the site of the debate where Mr. Santelli raised the monetary question.