Party unity is a key feature of the political landscape and an important element of the clarity and strength of party positions, but the critical question of how leadership and backbencher preferences feed into common positions is largely unasked. We argue that intraparty organization is critical both for party positioning and for the volatility of those positions. Whether and when backbenchers who would like to change their party’s position can gain the influence to put their desires into practice depends on how and to whom intraparty structure and process provide opportunities for influence. We model the incentives for party rank-and-file who might like to change their party’s position to nonetheless support leadership decisions. Contrary to veto-player theory, our model suggests that changes in party-label policy content should be more frequent in parties with more members in positions of influence. We test our model utilizing party-position data drawn from election manifestos.