We analyze a one-dimensional model of spatial political competition with two parties and uncertainty on the distribution of voters’ types. We assume that parties are formed by regular members and professional politicians; members care about the policy enacted, while professional politicians, on the contrary, care only about winning the election. We consider two possibilities: that members choose the political platforms and that professional politicians are the ones who choose such platforms. The expected utility for party members is analyzed under these two cases. We find that when professional politicians have no informational advantage, it is on the interest of both parties to let professional politicians choose the platforms. Only in the case in which professional politicians have much better information than the members of the party about voters is it possible that party members obtain a greater expected utility choosing the platforms themselves rather than letting the professional politicians choose.