S&P 500's 13.7% Post-Midterm Rally Faces a 2026 Reality Check

By Nathan Brooks

The S&P 500 has gained an average of 13.7% in the year after every midterm election since 1980, according to a CNBC analysis — but strategists say 2026 may break the pattern.

The Pew Research Center calls this year's midterms "uniquely difficult" to predict, and that label applies to markets as much as to pollsters. History is on investors' side; the current backdrop is not.

Over the past 70 years, U.S. stocks have mostly risen in the months between midterm elections and year-end. That tailwind has made the post-midterm stretch one of the most reliable seasonal trades on the calendar. Roughly speaking, it's the kind of pattern practitioners used to bank on almost mechanically.

Why 2026 looks different

What does this change for investors? The usual seasonal playbook assumes the election removes uncertainty. This year, the vote may add to it.

Three unresolved overhangs sit squarely in front of the market:

• Oil and Iran. It remains unclear whether the war in Iran will keep pushing already-soaring oil prices higher.
• Inflation and the Fed. Investors can't yet price whether inflation resolves on its own or forces an interest rate hike from the Federal Reserve.
• Tech and AI spending. The tech sector is under pressure amid growing concerns about runaway spending on artificial intelligence, with tech stocks and crypto already sliding.

Any one of these could move markets on its own. Stacked together, they make the historical average a weak guide.

An unusually wide political map

The ballot itself is bigger than usual. All 435 seats in the U.S. House of Representatives and 35 in the U.S. Senate are in play, according to the Taubman Center for American Politics and Policy at Brown's Watson School of International and Public Affairs.

Voters will also decide 36 state governorships, thousands of state legislative seats and 145 state ballot measures, per the Taubman Center's tally of Ballotpedia data.

"The 2026 election is among the most consequential in decades," said Eric Patashnik, a political science professor and director of the Taubman Center. "Understanding how the U.S. political system works—and why our governing institutions are struggling to solve the problems Americans care about—has never been more urgent."

A number of races remain too close to call. The central question for markets: whether Democrats take back control of the House — and possibly the Senate.

Which sectors carry the real risk?

A rally is one possible outcome, and history says it's the base case. But a Democratic sweep in one or both chambers of Congress would change the calculus for specific industries.

The exposed groups, per CNBC, are defense, healthcare, cryptocurrency and AI — sectors that are heavily connected to government policy. The mechanism is straightforward: a Democratic Congress could empower the party to investigate U.S. companies, a lever already visible in current tariff and oversight fights.

That's why even the experts won't call the direction. As the source puts it plainly: even for experts, it's impossible to predict.

The practical read

For portfolio managers, the honest framing is this: the 13.7% post-midterm average is a real number from a real sample — 40-plus years of it — but it's an average drawn from cycles that lacked an oil shock, an unresolved rate question and an AI spending reckoning running simultaneously.

The sector-level split matters more than the index-level story this time. Investors with concentrated exposure to defense, healthcare, crypto and AI names face election-specific headline risk, while broad-index holders are betting the historical pattern holds through an unusually noisy backdrop.

Either way, the days right after the vote — when the 435 House races, 35 Senate contests and 145 ballot measures resolve — will do more to set the tone than any pre-election positioning.