Wall Street is grappling with two contradictory post-midterm signals this week: a broad rally on Wednesday, November 4 that sent the Dow Jones up 3.03%, followed by a $3.2 trillion rout on Thursday that knocked the Philadelphia Semiconductor Index down 12% — its second-largest decline on record — and left investors asking whether the historically reliable post-midterm bull run still applies, Boursorama reported in a column by Reuters’ Jamie McGeever published Friday, November 7.
Democrats swept to majorities in both chambers of Congress on Tuesday, ousting Republicans in an election Donald Trump’s party lost decisively. The immediate read from traders was relief — until Thursday, when investors repriced the risk that a Democratic Congress could slow the frantic buildout of artificial-intelligence data centers, the single largest driver of US equity gains this year.
The following data supports the optimism, but also reveals where it fails.
AI Capex Risk Outweighs Midterm Election Gains
- Since 1946, the S&P 500 has risen in the 12 months after every midterm election, averaging a 14.4% gain — a 100% hit rate, per Deutsche Bank data cited by Boursorama.
- Thursday’s semiconductor plunge (-12%) and Wednesday’s defense-stock losses (Lockheed Martin down 6.95% per AFP) show the market is now trading on AI capex risk, not election math.
Wednesday: The Textbook Rally, in One Session
The initial reaction fit the historical playbook exactly. On Wednesday, the Dow gained 3.03%, the Nasdaq rose 1.44% and the S&P 500 added 1.58%, AFP reported via Medias24. The 10-year Treasury yield eased to 4.89% from 4.96%, and Brent crude dropped 8.67% to $94.62, its lowest since early September, Boursenews.cma’s market wrap showed — a combination Interactive Brokers’ Jose Torres called “a powerful rebound on Wall Street,” driven by falling oil prices and declining rates.
“Midterm election uncertainty is behind us,” Torres said, per AFP.
Thursday: Where the Old Playbook Snaps
But the balance sheet tells a different story. Overnight futures had alreadyfallen hard on results night, weighed down by fears that Democratic wins in key states like Texas could slow AI data-center permitting, Briefing.com analysts said, per AFP. Semiconductor names bore the brunt: Nvidia closed down 3.17%, Micron fell 7.00% and Intel lost 3.77% on Wednesday, even as megacap buyers of AI infrastructure rallied — Meta gained 1.44%, Apple 5.31%, Amazon 6.12% and Microsoft 6.68%. By Thursday, the SOX index’s 12% drop wiped out $3.2 trillion of Wall Street value, Boursorama’s column states.
Interactive Brokers’ Steve Sosnick offered the counterintuitive reading of the regulatory threat: “In a way, people are welcoming the idea that the sector could be protected from its worst instincts” — arguing tighter AI oversight would limit the overinvestment risk that has worried Wall Street for weeks.
The Historical Case, Quantified
Since 1949, the S&P 500 has gained an average of just 8.4% in midterm election years, as pre-election uncertainty suppresses returns.
| Period | Hit rate | Mean gain | Median gain |
|---|---|---|---|
| Any calendar year (post-WWII) | 71% | ~9% | 11.6% |
| 12 months after midterms (1946–2022) | 100% | 14.4% | 13.7% |
| Third year of presidential cycle (since 1950) | No recessions | 20.9% | — |
Three Cracks in the Scenario
First, the market entered this election year already strong — the S&P 500 had been propelled to record highs ahead of the midterm elections — limiting the fuel for outsized follow-through gains. Third, and most consequential: US equity concentration has never been higher.
The AI buildout behind that concentration is estimated at more than $10 trillion in spending between 2025 and 2032, funded increasingly by debt. McGeever’s framing: is this a worse misallocation of capital than the dot-com boom, whose parallels — transformative technology, excessive spending, “irrational exuberance” — ended in a spectacular crash a quarter century ago?
Then there is the Fed. It delivered a sharp drop in oil prices, and the ten-year Treasury yield eased back to 4.88% from 4.96% the previous day.
What History’s Two Exceptions Look Like
If the post-midterm pattern holds and the US avoids recession in 2027, investors could see an exceptional year. But the AI turbulence now shaking technology valuations sits upstream of the broader economy, McGeever writes: given how central the AI investment boom is to Wall Street and to US financial health, an abrupt slowdown could put the “R word” front and center.
