A monthslong selloff in government bonds is skidding into dangerous ground, pushing borrowing costs toward levels that some fear will finally damage the stock market and the economy.

Yields on U.S. Treasurys, which rise when bond prices fall, surged anew on Thursday, lifted by a new jump in oil prices, a firm wholesale inflation report and President Trump's promise to send $5,000 checks to Americans if Republicans keep control of Congress-a pledge that would add more than $1 trillion to the federal deficit.

Bond yields have been climbing since late June, breezing past Treasury Secretary Scott Bessent's efforts to stem the rise through increased government buybacks of its own long-term debt. Along the way, the bond markets have crossed milestones unseen in months, and even years. The yield on the 30-year Treasury bond has already reached 19-year highs.

Now, though, all eyes are on the ultimate benchmark.

Mortgages. Student loans. Corporate bonds-interest rates on all forms of debt are linked closely to the yield on America's 10-year Treasury note, which is now on the brink of 5% for just the second time since the 2008-09 financial crisis. Sam Stovall, chief investment strategist at CFRA Research, thinks nothing good will come with a 10-year yielding 5%.

"I think that 5% is an emotional threshold above which investors would become increasingly concerned," he said. "That could lead to additional softness in the market."

Rising Treasury yields not only help lift borrowing costs for consumers and companies, but they also draw in investors who might otherwise shop for riskier assets, like stocks.

So far, little has seemed to faze the stock market, which has traded near record highs all year even as war raged in the Middle East and inflation inched higher stateside. Strong corporate earnings have helped power stocks through those headwinds. Lately, though, the rally has sputtered; all three major indexes are down this month.

For bond investors, the backup in yields echoes the fall of 2023, when the 10-year yield also crossed over 4.9%, and even touched 5% briefly. Then, on the day they crossed that threshold, bonds staged a furious rally to close below 4.9%.

Now, as in October 2023, some investors might be waiting to hit 5% before they start snapping up bonds. But there are reasons they might not this time. For one thing, though anxieties are rising, most investors aren't as concerned now that higher yields would lead quickly to a sharp slowdown in growth.

In addition, the protracted conflict between the U.S. and Iran, which many now fear could go on for years, is expected to leave energy prices higher for the foreseeable future-feeding into overall inflation and keeping the pressure on the Federal Reserve to raise interest rates.

As Brent crude rose another 6.3% to $107.63 a barrel on Thursday, many investors dialed up bets that the Fed will raise rates at its meeting next week-not even waiting for Friday's important consumer-price-index report. Interest rate futures showed a 71% chance of a rate hike, according to CME Group data, up from 61% Wednesday and 49% a week ago.

Just last week, Fed governor Christopher Waller, widely seen as an influential member of the central bank, said he would support holding rates steady if the CPI report shows core prices rising 0.2% from the previous month, matching economists forecasts. Investors, however, have put greater weight on comments made by Fed chairman Kevin Warsh at the Fed's Jackson Hole conference last month.

There, Warsh sounded so concerned about inflation that many investors thought he had painted himself into a corner, needing to raise rates this month whether the economy required it or not to maintain the central bank's credibility.

"The bond market is saying very clearly that the Fed is going to raise rates," said Ray Remy, vice chairman at Daiwa Capital Markets America. "The bond market's not waiting for tomorrow's CPI to make that determination."

Yields on Treaurys largely reflect investors' expectations for what short-term rates set by the Fed will average over the life of a bond. They in turn influence other borrowing costs. The average 30-year fixed mortgage rate ticked up to 6.76% this week, Freddie Mac reported Thursday, up from 6.71% last week

Faced with rising yields, Bessent last month made the surprise announcement that he would at least double buybacks of longer-term Treasurys, expanding a program that was originally intended to improve liquidity in older, off-the-run securities.

Bessent said early in Trump's second term that pushing the 10-year yield lower was a priority for the administration. He has explained his decision to expand buybacks by saying current yields don't reflect economic fundamentals-giving support to the view on Wall Street that he is at least trying to limit the rise in yields.

On that front, he has had decidedly mixed results. Since his original announcement, yields on longer-term Treasurys haven't climbed as much as those on short-term-term notes. But they are still moving higher, and did so even after the Treasury Department said it would buy up to $6 billion of longer-term bonds at its operation on Thursday-three times the previous maximum.

As it turned out, the government-which is supposed to only buy Treasurys at prevailing market prices-reported Thursday afternoon that it had only bought $5.2 billion of 10-year to 30-year Treasurys. That was a sign that it could have trouble buying as much bonds as investors have expected unless it relaxes guidelines on the prices it will pay.

Yields on longer-term Treasurys ticked even higher after that result. The yield on the 10-year note settled at 4.943%, its highest close since October 2023, up from 4.836% Wednesday, according to Tradeweb. The S&P 500 fell 0.6%, while the Dow Jones Industrial Average lost 317 points, or 0.6%.

Shares of companies sensitive to rate changes retreated. The Russell 2000 index of small companies declined about 1%, while the S&P's materials sector dropped 1.5%.

Stock investors have been grappling with the spillovers from the bond market turmoil while confronting a wall of worry built on sticky inflation, war-fueled rising oil prices and Fed interest-rate uncertainty. To make matters worse, September is historically the weakest month of the year for stocks, with investors returning from summer often resetting their positions.

Some stock investors are tuning out the bond market for now and looking ahead to Friday's inflation report-and next week's Fed decision.

"Could the equity market move into a more protracted downturn if CPI is well out of consensus tomorrow?" said Mark Hackett, chief market strategist for Nationwide. "That's the bigger risk than the somewhat arbitrary nature of 5% yields."