Despite accelerating debt levels, the real yield on U.S. Treasuries remains low due to investors' desire for their extreme safety and liquidity services. Economic theory makes clear that the fiscal surplus as a proportion of the outstanding debt must average out to the real interest rate over time. Exploring these equilibrium relations in a change-point vector autoregression model, I estimate the state-dependent properties of U.S. inflation and its stance of fiscal policy that characterize long-term debt cycles. An archetypal debt cycle consists of alternating phases of persistent deficits and surpluses in tandem with alternating patterns of inflation and fiscal stance. In line with these key properties found in the data, I present a simple analytical model based on the fiscal theory of the price level where the household has a preference for holding government bonds. Determinacy admits a standard passive monetary policy coupled with a broad range of active fiscal policy. When the real interest rate falls below the economy's growth rate, permanent fiscal deficits can be sustained in the long run. The model explains why fiscal inflation has largely remained benign over the past two decades.