We use an analytically tractable, heterogeneous-agent incomplete-markets model to show that the Ramsey planner's decision to finance stochastic public expenditures implies a departure from tax smoothing and an endogenous mean-reverting force to support positive debt growth despite the government's precautionary saving motives. Specifically, the government's attempt to balance the competing incentives between its own precautionary saving (tax smoothing) and households' precautionary saving (individual consumption smoothing)---even at the cost of extra tax distortion---implies an endogenous, soft lower bound on the stochastic unit-root dynamics of optimal taxes and public debt.
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