Premiums on US sovereign CDS have risen to persistently elevated levels since the financial crisis. In this paper, we ask whether these premiums affect the probability of a US fiscal default, namely a state in which budget balance can no longer be restored by further raising taxes or eroding the real value of debt. To that end, we develop a tractable equilibrium macrofinance model of the US economy, in which the fiscal and monetary policy stance jointly endogenously determine nominal debt, taxes, and growth. While US CDS cannot be valued using standard replication arguments, we show how in our equilibrium model, CDS premiums reflect endogenous risk adjusted fiscal default probabilities. A calibrated version of the model is quantitatively consistent with high premiums on US sovereign CDS.