Major U.S. stock indexes have posted substantial gains during President Trump’s second term, which began in January 2026. Through September 4, 2026, the Dow Jones Industrial Average, S&P 500, and Nasdaq Composite had climbed 23%, 29%, and 35%, respectively. The rally has been supported by factors including artificial intelligence infrastructure development, strong corporate earnings results, and elevated share buyback activity driven by lower corporate tax rates.
However, several indicators suggest the market may face headwinds ahead. Outstanding margin debt has reached all-time highs, and long-duration Treasury bond yields have climbed to levels not seen since the financial crisis. Most significantly, equity valuations have become historically stretched. The S&P 500’s Shiller Price-to-Earnings Ratio, also known as the Cyclically Adjusted P/E Ratio, stood at 41.41 on September 4, 2026, approaching the bull market high of 42.84 set in June 2026 and nearing the all-time record of 44.19 from December 1999. This metric has averaged 17.42 over its 156-year history beginning in January 1871.
Historical precedent offers cautionary signals. On the six prior occasions when the Shiller P/E Ratio exceeded 30, significant market declines followed, with the Dow, S&P 500, and Nasdaq falling between 20% and 89%. During the dot-com era, when valuations were even higher, the S&P 500 and Nasdaq shed 49% and 78%, respectively. While the metric does not predict timing or specific catalysts, its track record suggests an elevated probability of substantial market weakness.
Nevertheless, historical data also provides a counterbalance. Analysis of market cycles since September 1929 shows that bear markets have typically lasted approximately 286 calendar days, whereas bull markets have averaged 1,023 calendar days. Market corrections and downturns are described as normal, healthy components of equity investing and have generally proven temporary in nature.
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