The stock market is not yet pricing in a Democratic sweep of Congress — despite some polls and most prediction markets pointing that way — so that scenario could weigh on share prices Wednesday, according to investors and analysts.

Republicans managing to keep control could cause a short-term relief rally, they said.

Short-term moves aside, the typical post-midterm pattern in the months ahead is bullish. But some wonder if the market could buck the positive historical trend this time because the S&P 500 is already up so much this year going into the election.

As far as certain stocks to watch, a big Democratic win on Tuesday night — especially in the Texas governor race — could add fuel to an AI stock sell-off on the notion that more data center restrictions would gain momentum nationally. Defense stocks could come under pressure on fears of limits on spending.

Expected stock market reaction

Polls are pointing to a Democratic victory in the House and a toss-up in the Senate. Prediction markets have been more favorable to Democrats, calling for a blue sweep.

While investors are signaling "begrudging acceptance" to a base case scenario that there will indeed be a Democratic sweep, that's not how they're positioning, said Tobin Marcus, head of U.S. policy and politics at Wolfe Research. The firm's recent survey data among more than 100 institutional investors suggests they are not strongly positioned for any particular result.

"Investors seem to have a significant dose of skepticism about whether the final outcome is going to be quite as favorable to Democrats as the polling suggests," Marcus told CNBC, noting that the firm shares the view that the "polling is likely overstating Democratic strength."

JPMorgan sees a blue wave knocking the S&P 500 by about a half percent on Wednesday.

On the other hand, if Republicans end up retaining both chambers of Congress, that could spur a rally, said Sameer Samana, head of global equities and real assets at Wells Fargo Investment Institute.

"From a certainty standpoint, the market knows what to do with Republicans holding both chambers," he said.

Citigroup strategists said Monday that Republicans losing the House but managing to keep the Senate could be "a tailwind for equities into year-end." JPMorgan traders predict up to a 1% pop on Wednesday if Republicans hold on to that chamber.

Looking past any short-term move, stocks tend to rally after the midterms have concluded. In fact, the S&P 500 was up one year out after all midterm elections going back to the early 1980s.

But the S&P 500 has already recorded double-digit gains so far in 2026, so some on Wall Street worry that investors are being overly complacent heading into this year's elections.

During midterm election years, the S&P 500 has typically averaged a 14% drawdown at some point in the second half of the year found Jonathan Krinsky, chief market technician at BTIG.

"The reason stocks often perform well in November during midterms is because [the S&P 500] typically is weak INTO the elections. We have the opposite setup this year," Krinsky wrote last week. "Therefore, while consensus is that we see a post midterm rally, we think the opposite is actually more likely."

AI jitters meet the ballot box

It's not helping that the broader market has recently come under significant pressure due to turbulence in the AI trade, which led the Nasdaq Composite to post its worst day since June on Friday. AI shares led the market lower again on Monday.

A strong showing from Democrats in Tuesday's midterm elections could pressure the trade even more.

At the state level, increased Democratic control is probably a headwind for stocks associated with data centers and technological capital equipment, analysts said.

"It [would solidify] the early kind of cautionary signs in different states around the advancement of AI infrastructure," Rob Rains at Washington Analysis told CNBC.

Goldman Sachs strategists said this week that a Democratic Congress "might limit data center tax incentives, but a national moratorium looks unlikely in any election outcome."

One example would be Texas — a key hub of the data-center buildout. A surprise loss there by Republican Gov. Greg Abbott has the "potential to spook" the market in the short term, Wolfe's Marcus said.

Defense and healthcare stocks

A blue wave might pressure defense shares, while boosting health care stocks, analysts and investors said.

"A substantial Democratic sweep could limit real spending growth unless a broader agreement increases both defense and health-care funding," said Alex Sagal, global equity analyst at Wells Fargo Investment Institute. However, he noted that the earnings outlook for the defense industry looks "stable to modestly positive."

Wolfe Research's Marcus said that healthcare is going to be "the biggest focus," as Democrats will push for restoring expired Affordable Care Act enhanced premium subsidies or unwinding some of the Medicaid reforms in the One Big Beautiful Bill Act.

"Healthcare stocks have been doing really well lately," Jed Ellerbroek, portfolio manager at Argent Capital Management, said to CNBC. "I think part of that is the anti-AI trade, but I also think part of it is just optimism that Democrats are taking over."

Ellerbroek is keeping his eye on hospital-related stocks such as HCA Healthcare and Tenet Healthcare as well as health insurers like UnitedHealth and Centene.

Bank pressure incoming?

Financials was the worst S&P 500 sector in early 2026 on the heels of President Donald Trump calling on Congress to pass a law that would cap credit card interest rates at 10%. While the sector has been able to notch gains since, with its year-to-date rise now at around 3%, things could get more unstable for the group under Democratic control.

"Democrats will come in wanting to show tangible progress on the affordability issue, and that means targeting sectors that are front and center in consumer budgets," said Evercore ISI's Matthew Aks. "We know Trump has populist instincts, populist leanings, and could he pick a couple of issues and decide to team up with the Democrats on those issues and target those industries in a populist way? Absolutely."

Given that Democratic control is often associated with increased regulation, while Republican control is thought to promote deregulation, Democrats could be interested in passing credit card rate caps if they come out victorious.

"I think if Democrats have control of one or both chambers, they would try to pass it and see if they could get Trump to either sign it or force him to veto it, and that would let Democrats kind of score a political point," Aks said.

Iran wildcard

Trump could restart the war against Iran after holding off any major strikes leading up to the midterms, a move that could upend the overall market and cause energy stocks to outperform. Crude oil prices jumped more than 10% in October, though they gave a lot of that gain back on Monday.

Gasoline prices stood at $4.17 a gallon on average nationwide Sunday, a nearly 40% increase compared to the same period last year, per AAA.

"If there are escalations, that could obviously put upward pressure on prices just ahead of Thanksgiving," said Patrick De Haan, head of petroleum analysts at Gas Buddy, "which is also when Americans have really staunch traditions in terms of driving to friends and family."

If Trump decides to take forceful action, it could snuff out hope for a typical post-midterm year-end rally.

Evercore ISI said the S&P 500 could retreat by double-digits to end the year at 6,800 as oil spikes if the president "moves to kinetic escalation in Iran ahead of seating the new Congress in January" and Democrats take Congress.

— With reporting by Sarah Min, Tobias Burns and Spencer Kimball