The literature on the great European parties of government is dominated by a business firm model, which emphasizes professionalism, the weakening of social ties, and de-ideologization of the internal competition. Contrary to these approaches, this article indicates that internal competition and struggles in a political party organized for the conquest of presidential power, such as the UMP, are not only generated by individual and electoral strategies. They are also motivated by social representations and identities, and they relate to socio-cultural dispositions and networks of recruitment of its members. Using the case of a mobilization fuelled by the comments on homosexuality (2005-2008) by the UMP member of parliament Christian Vanneste, the article examines the formation and politicization mechanisms and the logical of a conflicting partisan configuration.