The U.S. Treasury bought back $4 billion of outstanding government bonds on Thursday, marking one of the largest single-day debt repurchases in its history. The operation is part of the department’s regular liquidity-management program, which enables the Treasury to retire older, less-liquid securities and replace them with new issuance. Investor demand to sell was heavy: market participants tendered about $29 billion of bonds into the offering, far exceeding the amount the Treasury was willing to repurchase. Market strategists said the disparity underscores a search for liquidity in the wake of recent market volatility and highlights the growing scale of the Treasury’s daily buyback operations, which have now reached roughly $4 billion per session.