The risk of Tunisia’s nascent democracy falling to an incumbent takeover has declined considerably with the fragmentation of its autocratic successor party, Nidaa Tounes. What explains the many defections from Nidaa Tounes since 2014? While the popular wisdom would highlight President Essebsi’s attempts to elevate his son in the party leadership, we explore whether ideological and policy differences played a key role as well. We present an original dataset of the complete roll-call voting history from Tunisia’s first and second parliaments since the Arab Spring. Using this data and dynamic item-response theory, we examine whether MPs that were soon to break away from Nidaa Tounes had significantly different voting patterns than MPs who remained with Nidaa Tounes. Our research explores the internal mechanisms of autocratic successor party fragmentation in emerging democracies and also sheds light on why national unity governments so often fall apart.