WASHINGTON — Treasury Secretary Scott Bessent's decision to at least double the government's bond-buyback operations failed within 24 hours to bring long-term borrowing costs to heel, leaving the 30-year yield near a two-decade high as the department heads into 11 weeks before the midterm elections.

The Treasury Department said Wednesday it would at least double planned repurchases of longer-dated Treasurys from $2 billion to $4 billion between Sept. 9 and Nov. 4, an intervention aimed at supporting prices and easing yields that had climbed to multi-decade peaks. The 30-year yield eased to 5.18 percent after the announcement, from 5.34 percent on Tuesday, before bouncing back a day later, according to BBC News.

The rebound handed the administration an early rebuke from a market it had tried to steady, and it did so days after gross federal debt topped $40 trillion for the first time. That milestone, disclosed in Treasury figures released Wednesday, has sharpened investor scrutiny of long-dated U.S. paper at a moment when the department is issuing more of it and the Federal Reserve is holding rates.

The move

The Treasury said the enlarged operations reflected its "desire to provide greater liquidity support" for longer-term bonds and pledged to run them at "at least double" the current $2 billion pace between Sept. 9 and Nov. 4. Buybacks work by using cash to purchase outstanding Treasurys, tightening supply and lifting prices, which pushes yields down.

John Canavan, lead analyst at Oxford Economics, said the decision appeared to be an "attempt to provide relief" on long-term borrowing costs that had been under "significant pressure from rising oil prices, inflation risks and heavy supply due to global sovereign and corporate borrowing needs." Given the size of outstanding Treasury debt, he added, the increase was "unlikely to provide meaningful long-term relief."

Rene Albrecht, senior analyst at DZ Bank in Germany, said the Treasury feared the "pain of 5% or higher yields" because those levels raise borrowing costs for both the government and the private sector. "It's only three months until the midterm elections," Albrecht said. "They [the Treasury] have had to grab into the toolkit in order to get a hand on the recent rise in yields."

Yield curve control

Mohamed A. El-Erian, an economist at the Wharton School, said in a social media post that the operation raised the prospect of a broader effort to steer interest rates, an approach known as "yield curve control." The tactic can bring down longer-end yields in the short term and lower mortgage and other borrowing costs, he said, but "it risks collateral damage and unintended consequences."

The 30-year yield's 5.34 percent reading on Tuesday was the highest since 2007, driven by a global sell-off in long-dated debt that accelerated after the U.S.-Iran negotiating window expired without a deal earlier this week. Freddie Mac said the average interest rate on a 30-year fixed mortgage stands at 6.67 percent.

The debt backdrop

Treasury data showed gross federal debt reached $40.05 trillion on Aug. 18, more than double its 2016 level and closing on the $41.1 trillion statutory ceiling faster than the Congressional Budget Office projected. Interest payments on the debt now run about 15 percent higher than the same period last year and consume close to a fifth of tax revenue, "larger than defence," according to El-Erian.

Eric Swanson, an economics professor at the University of California and a former senior Federal Reserve economist, said the level of rates is what most separates today's debt from a decade ago. "Long-term interest rates in the US are at multi-decade highs," Swanson said, attributing the pressure to inflation worries and "the extreme levels of US government borrowing." He said investor appetite for lending to the U.S. government is diminishing, creating a "vicious" cycle that requires ever higher yields to place new debt.

The Fed sits still

Federal Reserve minutes released Wednesday showed several policymakers favored a rate increase at last month's meeting, though the central bank held its benchmark rate in the 3.50 percent to 3.75 percent range for a fifth consecutive meeting. Many participants said further increases would "likely be necessary if inflation did not decline." The Fed is expected to hold steady again at its September meeting.

Not a crisis yet

Some economists said the situation is not yet acute. El-Erian described the moment as "a flashing yellow light" and added, "It's not a flashing red light." Swanson noted that the U.S. debt-to-GDP ratio of about 126 percent trails Japan and Italy. Charlie Bean, an emeritus economics professor at the London School of Economics, said a threshold exists at which the market could turn on Treasurys but "unfortunately we don't know where it is." Les Rubin, writing in Fox News's opinion section, took the opposite view, calling the trajectory the late stage of a democratic decline and demanding congressional restraint; the wire coverage did not adopt that framing.

The enlarged buybacks are scheduled to begin Sept. 9. The Federal Reserve's next policy meeting is scheduled for September.