Four years into the current bull market, which began after the 2022 bear market ended, the S&P 500 and Nasdaq Composite have more than doubled and the Dow Jones has risen 84%, driven by AI infrastructure spending and record share buybacks. The article argues valuations are historically stretched: the Shiller P/E topped 41 as of Oct. 21, the second-priciest level in history, versus a 156-year average of 17.44. Since January 1871, the CAPE Ratio has exceeded 30 during a continuous bull market only six times, and the previous five were followed by declines of 20% to 89% in one or more major indexes. Outstanding margin debt hit a record $1.502 trillion in June 2026, up 77% since April 2025; after the three earlier surges of this kind peaked, the S&P 500 fell 49%, 57% and 25%. The article also notes that investors have historically overestimated how fast next-big-thing technologies get adopted.
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Related tickers and likely impact
QQQ
▼ Likely negativeInvesco QQQ Trust
Relevance: medium
| Market | US stocks |
|---|---|
| Sector | ETF |
| Close on 10/23/2026 | 704.39 |
| Change that session | -0.01% |
SPY
▼ Likely negativeSPDR S&P 500 ETF
Relevance: medium
| Market | US stocks |
|---|---|
| Sector | ETF |
| Close on 10/23/2026 | 759.85 |
| Change that session | -0.54% |
Impact is scored by AI from the headline and may be wrong. It is not investment advice.
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