Many political observers view get-out-the-vote (GOTV) mobilization drives as a way to increase turnout among chronic nonvoters. However, such a strategy assumes that GOTV efforts are effective at increasing turnout in this population, and the extant research offers contradictory evidence regarding the empirical validity of this assumption. We propose a model where only those citizens whose propensity to vote is near the indifference threshold are mobilized to vote and the threshold is determined by the general interest in the election. Our three-parameter model reconciles prior inconsistent empirical results and argues that low-propensity voters can be effectively mobilized only in high-turnout elections. The model is tested on 11 randomized face-to-face voter mobilization field experiments in which we specifically analyze whether subjects' baseline propensity to vote conditions the effectiveness of door-to-door GOTV canvassing. The evidence is consistent with the model and suggests that face-to-face mobilization is better at stimulating turnout among low-propensity voters in prominent elections than it is in quiescent ones.