Abstract: American postmodern author E. L. Doctorow reconstructs the Rosenberg case through multiple perspectives in The Book of Daniel, offering a penetrating reflection on the historical, political, and spiritual landscape of America from the 1930s to the 1950s. The essay takes radicalism as its central framework, tracing the historical evolution of this political tradition in Western and American contexts, and positions the Rosenberg case as the historical origin point of twentieth-century American radical politics. This establishes the novel's narrative structure, which juxtaposes the disillusionment of the Old Left with the reverberations of the New Left. The second and third sections focus respectively on the Isaacsons and on Susan, presenting the Old Left's disillusionment under the disciplinary force of political power, and the New Left's tragic self-destruction through radical resistance. The essay systematically examines the internal logic governing both generations' political beliefs and practices: the Old Left's fixation on collectivism and its ideological exclusivity; the New Left's political naïveté underlying its individualized resistance and the externally sourced nature of its programmatic action — both reflecting the deep and irreconcilable tension between radical thought and political reality. The essay further reveals that Doctorow, writing from the dual standpoint of a "radical Jewish humanist, " both critiques the shared limitations of two generations of radicals and compassionately upholds individual dignity, offering a significant literary hermeneutic path for understanding the intellectual evolution and historical fate of twentieth-century American radicalism.