Dizzying Week for Investors as Politics, A.I. and the Economy Collide With a lot of information to process in a short time, many market watchers said that the moves were extreme — in both directions.

S&P 500 index How stocks are trading in the United States Investors faced a whipsaw week in which stocks jumped after Democrats swept the midterm elections, then fell on renewed concerns over the artificial intelligence industry, and ended on Friday somewhere in between.

The S&P 500 index slumped to its fourth-straight weekly loss, of 2.7 percent, on Friday, its worst slide since the unveiling of President Trump’s tariffs last year. The index had gained as much as 1.8 percent and fallen as far as 3 percent for the week, the biggest range of movement in a single week since April.

Many investors and analysts said the market moves were extreme — both up and down. By Friday, some equilibrium appeared to emerge: The S&P 500 rose 0.3 percent, and the tech-heavy Nasdaq, which was at the forefront of a rout the day before, gained even more.

Investors have had a lot of information to process, seemingly all at once. Pre-election jitters gave way to a landslide victory for Democrats on a scale not seen in decades. The relief at a clear result quickly gave way to worries of tougher A.I. regulation, compounded by underwhelming earnings reports by some key industry players. And finally, on Friday, stronger-than-expected data on the U.S. labor market showed the economy remained solid.

“We are telling our advisers to buy the dips,” said Gene Goldman, chief investment officer at Cetera Financial Group. “The economy is not doing badly.”Others also saw opportunity in the upheaval, expecting stocks to bounce higher. “As painful as it sounds, I think this is a dip-buying opportunity, not the start of a large decline in A.I.,” said Tom Lee, co-founder and head of research at Fundstrat.

Broadly, investors and analysts said they expected the market to rally into the end of the year, with bouts of volatility along the way, as plans for how newly elected Democrats will oversee the A.I. build-out take shape. The current Republican-led Congress and White House have adopted a largely hands-off approach to the A.I. industry over the past two years.

“While we could see a period of market indigestion following the election results, we do not think fundamentals justify a prolonged downturn,” said Mark Haefele, the chief investment officer at UBS Global Wealth Management.

Investors were already on edge before this event-filled week, with periodic sell-offs reflecting concerns about the A.I. industry’s performance, despite bumper profit reports from many of the companies at the forefront of the technology.

A rush to build data centers had led companies to borrow enormous sums in debt markets, with no promise that returns would later justify the expenditure. And with companies all trying to grow at the same time, supply chain bottlenecks had put real-world constraints on those aggressive business plans.

Then there were the midterms, with the potential for a contested result and legal challenges, and the outlook for other important market factors, like the war with Iran and the path of interest rates, hanging in the balance.

As the voting result became clear, stocks rose on Wednesday in what traders call a “relief rally,” fanned by a surge of buying from investors who had been waiting on the sidelines until the campaign was over.

A day later, that exuberance began to fade. Two chipmakers, Qualcomm and Arm Holdings, had reported earnings that fell short of expectations, dragging down others in the industry, including heavyweights like Nvidia, which exert a heavy influence on market indexes.

Analysts assessing the financial impact of the Democrats’ electoral sweep pointed to a fundamental, though still modest, reassessment of the growth prospects for A.I. businesses. The shift in power at statehouses around the country led many to suggest that stricter regulation of data centers could slow plans in places like Texas, where the world’s largest tech companies are rapidly building out computing capacity.

The S&P 500 opened slightly lower on Thursday, but the sell-off quickly gathered speed, extending into more panicked trading that fed off investors’ long-held concerns about the assumptions underlying the lofty valuations of some A.I. companies. The S&P 500 ended the day with its largest decline in nearly two years. The fallout reverberated around the world.

Markets across Asia, which were closed during the worst of the selling on Wall Street, had a chaotic open to trading on Friday. The severity set off a 20-minute trading halt at the tech-heavy KOSPI, which plunged 6 percent by the end of the session, pulled down by the memory-chip makers SK Hynix and Samsung Electronics. Japan’s benchmark Nikkei 225 sank about 6 percent, dropping the index into a bear market, defined as a 20 percent fall from its recent peak.

But as trading got underway in Europe the tide began to turn, with some semiconductor companies in the region posting gains.

The latest U.S. jobs report, released before U.S. markets opened on Friday, also eased investors’ worries. Employers added 165,000 jobs in October, more than analysts were expecting, and the unemployment rate dropped to 4.1 percent.

When Wall Street began trading, markets stabilized. The Nasdaq rose more than 1 percent, driven by a rebound in chipmakers. Nvidia gained roughly 3 percent, reversing some of the previous day’s loss.

For Mohit Kumar, a strategist at Jefferies, the recent turmoil was not a sign of the unwinding of the A.I. trade, even if it is subject to tougher oversight in the years ahead. “One could argue,” he wrote in a research note, “that having more guardrails makes A.I. investment more sustainable in the medium term.”Joe Rennison writes about financial markets, a beat that ranges from chronicling the vagaries of the stock market to explaining the often-inscrutable trading decisions of Wall Street insiders.