There are lots of things that can move the stock market, from economic data, to Federal Reserve pronouncements, to corporate developments. But for the past 15 months, traders’ fortunes have been largely tethered to the whims of a single person: President Donald Trump.

Since taking office last January, Trump’s comments to reporters in extemporaneous gatherings in the Oval Office and at formal press conferences, as well as his posts on social media, have been the primary driver behind the five best and worst days in the S&P 500 Index, according to an analysis from Fundstrat Research. It’s a grip unmatched by any modern American leader. No other president has orchestrated this many best and worst days in a dozen administrations going back to President Ronald Reagan in 1981.

“He has the market in a chokehold,” said Hardika Singh, economic strategist at Fundstrat. “The president isn’t supposed to have such an extraordinary amount of control over the fortunes of the stock market. It’s completely unprecedented.”

The war in Iran is providing a perfect backdrop to see how much Trump can move U.S. stocks. The S&P 500 just posted its fastest V-shaped drop and recovery since 2020, tumbling 9% from a Jan. 27 peak to the cusp of a technical correction on March 30, before rallying back to all-time highs over the course of 11 trading days.

The impact of the president’s words is even clearer when examined session-by-session. For example, the S&P 500 sank 1.5% on March 20, as Trump said in a White House briefing that he didn’t want a ceasefire with Iran. Then, on March 31, the index jumped 2.9% for its best day since May and rallied through the rest of the week after Trump told reporters at several different news outlets that negotiations with Iran were going well and the war was close to ending. There are numerous similar examples from before and since then.

It isn’t just equities that are seeing these moves either. Commodity prices have also swung wildly, with oil market volatility rising to levels last seen at the start of the COVID-19 pandemic.

In essence, Trump’s wavering positions on the war have made him the market’s “arsonist and firefighter,” said Alexander Altmann, head of global equities tactical strategies at Barclays.

The whiplash strongly resembles last year’s tariff-driven rout and subsequent rebound. Both episodes were tied to abrupt policy jolts from the president and unwound by equally abrupt backpedaling. It has now reached the point where Wall Street is anticipating reversals in policy and rhetoric from day to day.

“Investors have been conditioned, not wrongly, to expect that if things get too bad, especially if it’s administration induced...they’re waiting for the tweet that says, actually, we’re good,” said Ross Mayfield, an investment strategist for Baird Private Wealth Management.

The president’s influence on stocks isn’t entirely new. Typically, the S&P 500’s biggest up and down days are driven by a combination of micro and macro catalysts, with Washington policy being one. What’s different about Trump’s second term is the market swings so closely track his social media posts and public speaking engagements.

“I have never seen a market that’s been this moved by chatter coming out of the White House on a daily basis,” said veteran market strategist Ed Yardeni of Yardeni Research. “Trump speaks every single day, and every single day he says something that seems to have an impact on the market.”

Trump’s fixation on equity prices as a scoreboard was well known before his second term began. Official White House social media channels are now using their platforms to address market moves, posting animated graphics to tout S&P 500 records or telling Wall Street not to be “panicans” when Trump’s words or policies spark fears. He’s even explicitly urged investors to buy stocks.

“If we look back again in data, this has never happened before,” Fundstrat’s Singh said. “That to me is just crazy.”

Among the S&P 500’s best days during Trump’s current term are the 9.5% rally on April 9, 2025, when he paused his tariffs, and the 3.3% jump on May 12, 2025, when the U.S. and China agreed to a 90-day trade truce. On the flipside, the worst days include the 6% plunge on April 4, 2025, after China retaliated with tariffs on the U.S., and the 4.8% drop on April 3, 2025, after the president first implemented sweeping levies.

Of course, some Wall Street pros argue that the symbiosis between what the president says and what the market does is purely anecdotal and a function of the frequency of the president’s communication.

For instance, a look at volatility measurements contradicts the idea that the market has been more turbulent under Trump than during past administrations, Barclays’ Altmann said. The average value of the Cboe Volatility Index, or VIX, across the entire term of each president since the inception of the gauge in 1990 is 19.3, precisely in line with Trump’s second term and with President Joe Biden’s term, according to his analysis.

“While the world may hang on to the unorthodox communication methods by the president, and anticipate a bout of market volatility in its wake, the reality is that markets are behaving in a consistent way with historic patterns,” Altmann said. “It is the medium — high cadency social media — by which it is reacting to news flow that has changed rather than the magnitude of the reaction.”

The rise of passive investing has made the market more reactive to news in general, whether it’s a president’s comments or an unexpected earnings report, said Michael Green, portfolio manager and chief strategist at Simplify Asset Management.

In the simplest terms, he explained, the computers that manage passive portfolios are being programmed to buy or sell assets based on headlines, which is driving moves in broader indexes. By his estimate, markets are approximately four to five times more reactive than they’ve been historically.

“The headline volatility from Trump just has to do with the fact that he’s speaking more frequently,” Green said. “The simple math is that he is just a guy born into a time.”

©2026 Bloomberg L.P. Visit bloomberg.com. Distributed by Tribune Content Agency, LLC.