The aim of this article is twofold. Firstly, it offers a new definition of ‘mainstream’.

Moving beyond understandings of the concept that focus exclusively on parties’

alternation in power, or their ideology/message, the article’s conceptualisation

considers both supply and demand sides of politics. Hence, an attitudinal

component to functional definitions is added. This implies that, to be called

‘mainstream’, certain attitudes must be shared by a majority of the public, and

there must be no significant differences in their endorsement across political

groups. Secondly, consideration is given to whether liberal-, social-democratic,

and populist radical right (PRR) parties and attitudes meet this new reconceptualisation.

While liberal- and, to a lesser extent, social-democratic parties and

attitudes are indeed shown to be ‘mainstream’, the PRR is found to fall outside

of the proposed definition, despite being ‘established’ on the supply side. The

article concludes by underlining its wider theoretical implications.