Expansionary fiscal policy lowers the return difference between public debt and less liquid assets - the liquidity premium. We rationalize this finding in an estimated heterogeneous-agent New-Keynesian model with incomplete markets and portfolio choice, in which public debt affects private liquidity. This liquidity channel stabilizes fixed-capital investment. We then quantify the long-run effects of higher public debt and find little crowding out of capital, but a sizable decline of the liquidity premium, which increases the fiscal burden of debt. The revenue-maximizing level of public debt is positive and has increased to 60 percent of US GDP post-2010.