Social networks are seen as less confortable for rulers than more traditional ways of communication. They equalize the balance of power between citizens and politicians. However, we will see in this article than social networks could also be a very powerful political communication tool in order to gather citizens in a crisis situation such as terrorist attacks. We will particularly focus on the communication of French President François Hollande on Facebook and Twitter during the terrorist attacks of novembre 2015. His tweet only few minutes after the end of the police intervention was shared 57 000 times, a record in french history of social networks. Nevertheless, we will see that the consensus around the president is less effective and lasting on social networks than on the other media.