From the introduction of The Debt Limit Since 2011 (Jan. 19, 2018 R43389):
On September 6, 2017, an agreement on the debt limit and a continuing resolution was announced between President Trump and congressional leaders. Two days later a measure (P.L. 115-56) was enacted to implement that agreement, which included a suspension of the debt limit through December 8, 2017. Once that suspension lapsed, Treasury Secretary Mnuchin invoked authorities to employ extraordinary measures. One recent estimate suggests those would last until sometime in early March and another indicated the critical date could fall between late February and late March 2018. Secretary Mnuchin reportedly asked some congressional leaders to act on the debt limit before the end of February 2018.