Furthermore, in the case of far-right, far-left and regionalism parties in the national parliaments of much of the European Union, mainstream political parties may form an informal cordon sanitarian which applies a policy of non-cooperation towards those "Outsider Parties" present in the legislature which are viewed as 'anti-system' or otherwise unacceptable for government. Cordon Sanitarian, however, have been increasingly abandoned over the past two decades in multi-party democracies as the pressure to construct broad coalitions in order to win elections – along with the increased willingness of outsider parties themselves to participate in government – has led to many such parties entering electoral and government coalitions.

Will mainstream political parties not cooperate towards outsider parties if they are too extream?