Can Monetary Policy Create Fiscal Capacity?

Governments around the world have gone on a massive fiscal expansion in response to the GFC and Covid crises, increasing government debt to levels not seen in 75 years. How will this debt be repaid? What role do conventional and unconventional monetary policy play? We investigate debt sustainability in a New Keynesian model with an intermediary sector, realistic fiscal and monetary policy, endogenous convenience yields, and substantial risk premia. During a large economic crisis, increased government spending and lower tax revenue lead to a large rise in government debt and raise the risk of future tax increases. Quantitative easing (QE) contributes to lowering the debt/GDP ratio and reducing the risk of future tax increases. QE is state- and duration-dependent: while a temporary QE policy deployed in a crisis stimulates aggregate demand, permanent QE crowds out investment and lowers long-run output.