President Trump’s Halloween party at Mar-a-Lago, set to the theme of “The Great Gatsby,” reenacted the decadence of that story’s licentious era: befeathered flappers shimmying in the crowd; gilded and onyx décor; scantily clad women posing in an enormous champagne coupe. The revelatory moment says so much about where we stand today — and what we could be lurching into next.

Published a century ago, F. Scott Fitzgerald’s “The Great Gatsby” captured the culture of an overheated economy on the brink of demise. Just as Jay Gatsby fell from the height of fortune to an ignominious death, the 1920s roared with financial overindulgence until the markets drowned in the Wall Street crash of 1929. The Great Depression followed, and the consequences for the global economy proved calamitous.

Today we find ourselves again dancing toward new highs in the stock market. Speculative money is once more pouring into risky investment schemes, with staggering sums of money being thrown at artificial intelligence and cryptocurrencies. But rather than heed a century of hard-won lessons, the Trump administration’s financial regulators are embracing dissolute policies to keep the punch flowing.

The financial excesses of 100 years ago teach us how high the costs of negligent oversight of our markets can be. When sentinels sleep, fraudsters flourish; their frenzied celebration of unreal profits pumps froth into the market; ultimately, with panic and pain, bubbles will burst. As stages of that cycle are recurring, we must decide whether to intervene now — or to mop up the mess later.

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