<p>The emergence and election of new parties challenging mainstream status quo in democratic countries is one of the most critical features affecting the definition of national security priorities today. While we know that these parties contest mainstream security policies, it is less clear how they do so and with which effects. This paper addresses these questions by exploring challenger parties’ effects on security discussions in a democratic multi-party system. I argue that challengers can prompt the reorganisation of the security agenda by introducing new issues and diminishing the political relevance of previous national priorities. In competition with mainstream parties to dominate the political agenda, challengers will act as political entrepreneurs who mobilise public discontent on neglected security concerns. This suggests that the conglomeration of issues at the centre of the security agenda changes following on broader political struggles between mainstream parties competing to maintain the status-quo and challengers pursuing innovation. I illustrate this argument through two instances of political entrepreneurs in Bulgaria, a context offering important precedents to explore these parties’ effects amid frequent domestic and regional transformations. The paper contributes to discussions about the sources, pathways, and implications of domestic sources of transformations for security affairs.</p>