Cobb and Elder (1983, 152) describe a link between agenda entrance, by which they mean inclusion in the list of issues that compels attention by a governmental entity, and issue expansion, which refers to the number of people mobilized around an issue. They see the issue expansion process as a key element in the destruction of systems of limited participator and argue that as a larger and larger circle of participants is mobilized, the strength of the subsystem is likely to be weakened. Yet there is a second manner in which issues may gain agenda entrance; venue shopping by strategically-minded political actors.
(Baumgartner and Jones, 1991: 1050)
Baumgartner, F and Jones, B. 1991. Agenda Dynamics and Policy Subsystems. Journal of Politics Vol. 53, (4). pp.1044-1074.
Cobb Roger W and Elder, C E 1983. Participation in American Politics: They Dynamics of Agenda-Building. Baltimore: The John Hopkins University Press.
see also: issue expansion, Confluence Points.