WASHINGTON—The U.S. Treasury could be able to fund government operations into the first half of January without a debt ceiling increase, according to a new estimate by money market research firm Wrightson ICAP on Monday. Wrightson said in a note to clients that based on the Treasury’s debt issuance plans, the department should be able to go well past a new Dec. 15 deadline set last week by Treasury Secretary Janet Yellen. She said that “under certain scenarios” the Treasury would lack sufficient resources and risk default after Dec. 15 after making a $118 billion transfer to the Highway Trust Fund. Yellen again urged Congress to increase or suspend the debt limit as soon as possible, but a longer deadline would provide Democrats more room for maneuvering as they struggle to pass a sweeping, $1.75 trillion social and climate spending bill without Republican votes. “Our own updated base case is …