May 18th, 2003: the Peronist Nestor Kirchner unexpectedly became the first Argentinian President to be legitimized by general elections since the very serious political, economic and social crisis that the country had experienced two years before. This paper looks back on the exceptional victory of this outsider, as well as on the way he then succeeded in reproducing some political credibility within a very short period of time. To do so, he carried out a reform of the military institutions inherited from the dictatorship, twenty years after the restoration of democracy. By taking this paradoxical stand, Nestor Kirchner managed to build up a network of political allies and social supports around him, which proved essential to the consolidation of his authority.