The bull market in stocks has a new headache.

Government market interventions this summer in the U.S., to cap long-term interest rates, and in Japan, to halt its currency’s decline, have given way to a stronger yen and higher Treasury yields. That combination could put the nearly four-year rally in the stock market in jeopardy.

Long-term Treasury yields were climbing again on Wednesday. Global oil prices shot above $100 a barrel as the Iran war drags on. And the Japanese yen, once the world’s cheapest funding currency, was gaining against the U.S. dollar.

None of those factors in isolation have prompted a lasting impact on the U.S. stock market, which has been riding the high of the historic artificial-intelligence race. Yet their collective advance has suddenly turned up the anxiety level on Wall Street about the potential for a violent blowback in the stock market.

Take Wednesday’s reaction to the Treasury Department’s decision to buy back to $6 trillion in long-term U.S. government debt — the first beefed-up buyback operation since Treasury Secretary Scott Bessent surprised the market with his intervention plans in mid-August.

Despite an increased size of buybacks, the announcement underwhelmed traders, sending the 10-year Treasury yield to 4.836%, its highest level since October 2023. Bessent might want lower yields, but the market just made it more expensive to borrow.

Rising Treasury yields can threaten the stock market in several ways, including by making the safety of government bonds more attractive than riskier equities. Higher rates also mean increased corporate borrowing costs, especially for the “hyperscalers” borrowing heavily to fund the AI data-center build-out.

“It’s still early days on how they are going to try to manage this,” said Dustin Reid, chief fixed-income strategist at Mackenzie Investments. “Certainly, the Treasury is not going to be overly thrilled with the reaction today.”

Adding to the risks for stocks is a stronger yen on the heels of the recent U.S.-Japan intervention in the foreign-exchange market, which could deal a blow to the popular yen “carry trade” on Wall Street. Typically, the trade involves borrowing lower-yielding yen to buy higher-yielding U.S. dollars, then using those dollars to invest in U.S. assets, such as technology stocks.

Any unwinding of the trade could spell trouble for AI and technology stocks. The one-two punch of a stronger yen and higher Treasury yields could be even worse for stocks.

“This is the greatest risk to the bull market,” said Jordan Rizzuto, chief investment officer at GammaRoad Capital Partners, on Wednesday.

While the size of the buybacks are small relative to the total size of the $31.5 trillion Treasury market, the Treasury Department has sent an important signal to the market. “We now know the Treasury’s current pain point at the long end of the curve,” Rizzuto said, speaking to the 10-year yield’s recent climb above 4.75%.

Earlier this week, Bessent challenged traders to “bet against me if you want.” He could now be forced to keep increasing the size of Treasury buyback operations to contain long-dated yields.

The tumult comes as the 10-year yield was moving close to the widely watched 5% threshold, which many see as a stumbling block for stocks. The 30-year Treasury yield, at 5.285%, was on the doorstep of its two-decade peak above 5.30% reached last month, according to FactSet data. Bond prices move in the opposite direction of yields.

Weakness in the Treasury market comes after the Netherlands’ central bank decided to move more of its gold out of New York to London. The central bank told MarketWatch the move will make it more easily tradable in a crisis. That raised fresh concerns about the appeal of U.S. assets in a fracturing world — and one where yield is no longer hard to find.

Recent data from Japan showed its holdings of foreign securities fell by almost $88 billion at the end of August. Japan has long been a significant owner of U.S. Treasurys.

If Japan recently sold U.S. debt assets, that’s noteworthy because it comes despite recent U.S. actions prop up Japan’s currency, noted Rizzuoto. “That gives you a sense of the gravity and weight of these two things,” he said.

On the one hand, the Treasury would want a yen that’s strong enough to reduce the likelihood that Japan needs to sell Treasury holdings to raise cash. But if the currency becomes too strong, that would increase the risks of another painful unwind of the yen carry trade.

The Japanese yen on Wednesday extended its rally against the U.S. dollar — hitting a session low of ¥153.49 per buck, after posting its strongest level since February in the previous session, according to FactSet data.

The yen now looks to be getting enough positive momentum where you could see a shakeout of some people who borrowed in yen to make leveraged bets on highflying U.S. stocks, said Steve Sosnick, chief strategist at Interactive Brokers.

Meanwhile, the Bank of Japan is expected to deliver an interest-rate hike next week, which has been driving the yen rally. There’s also been speculation that Japanese authorities might quietly intervene again in foreign-exchange markets to further curb the yen’s downturn since September.

U.S. stocks fell for a third session in a row on Wednesday, with the Dow Jones Industrial Average down more than 400 points, or 0.8%, while the S&P 500 edged 0.5% lower and the Nasdaq Composite was off 0.6%, according to FactSet data.