It might seem that Herbert Marcuse was right: leftist politics can no longer avoid the challenge of devising its own positive normative grounds. The neoliberal political rationality that is now hegemonic must be taken on by a new imaginary: radical, leftist and democratic. This article explores what major theories about new populism have to offer to a radical leftist attempt to reinvent itself. The regeneration of populist movements across the globe appears to offer signposts to guide a new radical politics. Yet I argue that populism is no ideologically empty mobilizing strategy able to be harnessed to all manner of political purposes. Embedded in its demagogic form are key presumptions about the character of democratic justification that collude with a neoliberal political project. Theories of new populism help us to shed light, instead, on the challenges that face the Left in its own self-reconstitution amidst liberal democratic crisis. Circumspection concerning the ideological load that is carried by a populist rendering of democratic politics needs to be united with an insight into how the rise of populism itself issues a warning about aspects of a social democratic past that cannot be reclaimed unchanged.