Donald Trump’s big economic speech Monday at Detroit offers a chance to get past the dodge that this race is about merely the character of the candidates and to address what William Galston of the Wall Street Journal calls the “real debate under the mud.” Both candidates are running a protectionist campaign, but on taxes, spending, and monetary policy, Mr. Trump has hinted at policies that hold far more promise for change on jobs and growth.

Growth — or the lack of it — has emerged as such an undeniable issue that the New York Times is trying to palm off on its long-suffering readers the suggestion that it has nothing to do with policy errors. Rather, the Gray Lady reckons, it’s a global phenomenon that started long before President Obama (though average quarterly GDP growth under Mr. Obama has been the worst of any of the last eleven presidents).

The big opening for Mr. Trump lies in the question of when this problem started. The Times publishes a marvelous chart showing when this decline in global growth began. It shows three downward sloping lines. Angel Collinson herself (please see above) couldn’t have skied them at their steepest. The three lines are for Europe, Japan, and America. They all portend the disaster we’ve inherited these past eight years.

The thing to mark is when the decline started. It was in the early 1970s. What happened then? That was when America defaulted on the obligations it had undertaken under the Bretton Woods system, which established a gold exchange standard. It wasn’t a gold standard of the classical type. But it did obligate America to hand over an ounce of gold for every 35 dollars presented to it by participating foreign governments.

After our default, we entered the era of fiat money, in which a dollar is not defined in law as any specific weight of gold (or silver). This has changed the whole incentive structure of the American, and world, economy, and the era of the casino economy began and average growth rates started their downhill slide, at home and abroad. It’s not just growth, either. It’s all sorts of other measures of economic performance.

During the era of Bretton Woods, unemployment averaged 4.6 percent. Between the end of Bretton woods and today, closer to 6.4 percent. The personal bankruptcy rate, on which Elizabeth Warren, a professor of bankruptcy law, likes to focus, had been steady for decades. Then suddenly — in the 1970s — it began soaring, and has yet to retreat. The inequality rate, on which Thos. Picketty likes to focus, also began soaring in the 1970s.

The opening for Donald Trump here is simple. Congress has already awakened to the idea that fiat money lies at the bottom of our economic problems — and the international nature of the problem that is underlined, but not discussed, in the Times. Within two weeks of Paul Ryan acceding to Speaker, the House passed and sent to the Senate the Fed Oversight Reform and Modernization Act. The measure is now before the Senate.

One of the things the FORM Act would do is establish a new monetary commission to conduct a strategic review of how monetary policy has been working since the century ago when we created the Federal Reserve. Mr. Obama has threatened to veto it. The opportunity for Donald Trump is to vow to sign this measure and formally open up the question of monetary reform. He is the right man to do it, because he understands the problem of currency manipulation.

Mr. Trump has shown a willingness to challenge all of the post-World War II structures — the United Nations, the North Atlantic Treaty, the North American Free Trade Agreement, among them. But none are as fundamental to the problems he wants to address as is the scourge of fiat money. If Mr. Trump can mark this point in Detroit, as he deals with taxes and regulation, he will get past the mudslinging over character and return the campaign to the main issue.