"The Constitution grants Congress the power to borrow money on the credit of the United States-- one part of its power of the purse--and thus mandates that Congress exercise control over federal debt. Control of debt policy has at times provided Congress with a means of raising concerns regarding fiscal policies. Debates over federal fiscal policy have been especially animated in the past decade, in part because of the accumulation of federal debt in the wake of the 2007-2008 financial crisis and subsequent recession. Rising debt levels, along with continued differences in views of fiscal policy, led to a series of contentious debt limit episodes in recent years. The debt limit is currently suspended through March 1, 2019. The limit will then be reset at a level that accommodates federal obligations incurred during the suspension period. The U.S. Treasury will then use cash balances, incoming revenues, and extraordinary measures to meet federal obligations. One estimate suggests those resources would suffice to cover federal payments until August, if not later."
CRS Report for Congress, R43389
Congressional Research Service: https://crsreports.congress.gov/