WITH HIS characteristic blend of aggressiveness and generality, President Trump has vowed to do “a big number on Dodd-Frank,” the 2010 financial regulation law enacted to prevent a repeat of the 2008 financial meltdown. On Friday, he signed an executive order setting in motion a four-month review process with an eye toward achieving that. Certain parts of Dodd-Frank, do, indeed, cry out for a fix. The measure may be unduly onerous on smaller banks that pose no real risk to overall financial stability. The Volcker rule, intended to force a clean break between commercial banks and their speculative “proprietary trading” desks, turned into page after page of impenetrable definitions and exceptions.

Yet in one fundamental respect, Dodd-Frank has helped make the financial system safer: boosting the capital of the largest banks. Banking experts generally agree that strong capital cushions are the simplest, most efficient means of ensuring solvency through a crisis. In the fourth quarter of 2015, the six largest financial institutions held high-quality capital worth roughly 12 percent of their assets, compared with just under 8 percent on the eve of the crisis. This is a major reason that the latest Federal Reserve “stress tests,” conducted pursuant to Dodd-Frank in June 2016, found that the banking system could withstand “a severe global recession with the domestic unemployment rate rising five percentage points.”

And so it was worrisome to hear the president’s point man on financial policy, National Economic Council Director Gary Cohn, take repeated shots at these heightened capital requirements, blaming them for the nation’s still-tepid growth rate nearly a decade after the crisis. “What is happening now, because of all the regulation, is that the Fed is pumping money into the banks, but the same Fed on the other side is telling all those banks you need to hold more and more and more capital, so that capital is never getting out to Main Street America,” Mr. Cohn told the Wall Street Journal. Really? According to the most recent data from the Federal Deposit Insurance Corporation, bank lending grew at a 6.8 percent annual rate in the third quarter of 2016. Quarterly bank profits, meanwhile, were more than double what they were at the time of Dodd-Frank’s enactment.

Yes, that lending growth rate was still below the pre-crisis level — but that’s just the point. Perhaps banks should be expanding credit a bit more slowly than they did during what turned out be an unsustainable bubble. Financial regulation’s goal is not maximum short-term growth, it’s maximum short-term growth consistent with long-term financial stability. Strong capital requirements are essential to achieving that, as the crisis taught. No doubt there’s a natural human tendency, post-crisis, to forget such lessons, or to play them down. That tendency is especially prevalent on Wall Street, where Mr. Cohn has spent his career. His words, unfortunately, suggest that the Trump administration may succumb to it.