In general, avoid this description in favor of a more precise definition of an individual’s political views.
When used, it suggests that an individual believes change must be made by tearing up the roots or foundation of the present order.
Although “radical” often is applied to individuals who hold strong socialist or communist views, it also is applied at times to individuals who believe an existing government must be replaced by a more authoritarian or militaristic one.
See also, AP Style leftist, ultra-leftist and AP Style rightist, ultra-rightist.