The statutory debt limit restricts the amount of funds that can be borrowed to meet the government’s obligations. The Fourteenth Amendment’s Public Debt Clause mandates that all the government’s legally authorized obligations be met. This article argues that the Clause protects these obligations from actions that create “substantial doubt” about their validity, including actions short of default or repudiation. The article proposes a test to determine substantial doubt that analyzes (1) the political and economic environment at the time of the government’s actions, and (2) the subjective apprehension exhibited by debtholders. Applying this test, the article argues that Congress’s actions in the 1995–96 and 2011 debt limit debates violated the Public Debt Clause. It argues, moreover, that the president must disregard the debt limit under circumstances, such as these, when the government’s actions have placed the validity of the debt in substantial doubt. This presidential duty arises from the Constitution and the Impoundment Control Act, both of which require the president to spend appropriated funds and ignore the debt limit in these situations.