This paper assesses the Granger causality between government spending and gross domestic product (GDP) in the United States at multiple horizons. This paper also analyses the role the real exchange rate plays in the causality measure during the zero lower bound (ZLB) period. Many researchers using theoretical models built in a closed economy suggest that the elasticity between government spending and GDP is very large, when the nominal interest rate is binding. Other researchers, also using theoretical models generally built in an open economy, suggest that the elasticity in the ZLB period is not large. The same conflicting results are reported in the empirical literature mostly using vector auto regressives (VARs), with different restrictions. In this paper, we use a different approach to measure the link between the two variables. The new approach has the advantage of not relying on any restrictions, as is the case with VARs when dealing with causalities. Moreover, our approach is not related to the way the model is built, as is the case with dynamic stochastic general equilibrium (DSGE) types of models. In this paper, we use a Granger causality measure to compare the causality for normal periods with the causality for the ZLB period. We emphasize the role played by the real exchange rate. Our empirical results provide evidence that the causality measures between government spending and GDP are larger and persistent in the ZLB period, but only if the exchange rate is not taken into account. When the exchange rate is taken into account, our measure of causality becomes very small and non-persistent.