This paper provides a comparative archival case study of Egyptian and Jordanian foreign policy in the build-up to the 1967 Six Day War. It investigates the ways in which President Nasser and King Hussein were pushed towards war by domestic forces, in particular, the security apparatuses that fortified their rule. More importantly, the paper explores variation in American and Israeli awareness of these domestic constraints: though each leader faced near-mutinous internal pressure from their top brass to confront Israel, U.S. and Israeli intelligence were clearly more attentive to Jordanian military pressure than Egyptian. What explains this variation, and how did it affect Israel’s treatment of the respective belligerents? At stake is the viability of Audience Cost Theory (ACT), a prominent International Relations theory on credible signals of resolve during crisis bargaining. According to ACT, leaders who demonstrate that they will be punished domestically if they back down from foreign policy threats will be taken more seriously. While ACT proponents usually conclude that democracies should issue more credible threats, this paper offers a new authoritarian audience cost mechanism. First, I argue that authoritarian militaries act as potent domestic audiences to leaders’ foreign policy decisions; authoritarian rulers must heed the foreign policy preferences of their security apparatus, or risk their downfall by coup d’état. I then argue that the transparency of these audience costs depends on two conditions, which constrain the autocrats’ ability to signal that his hands are tied without fear of exploitation by his opponents. First, does the opponent believe that the autocrats’ likely replacement would be more threatening than the current regime? Second, does the autocrat have reliable allies through which he could signal his vulnerability? The case studies, which rely on both declassified U.S. diplomatic cables (FRUS series) and authoritative historical accounts of the conflict, provide evidence of these dynamics. While Egyptian President Nasser’s hands were tied on the inexorable march to war by key military elites, he was unwilling and unable to signal these constraints—as a result, Nasser received no bargaining advantage. In contrast, Jordanian King Hussein used his comparatively friendly relationship with Israel and alliance with the United States to repeatedly signal his vulnerability to a nationalist military coup. This signaling won Hussein extraordinarily leniency from the Israelis, who only engaged with the Jordanians following Hussein’s fateful decision to relinquish control of his army to Egyptian command.