Frank Aiken was primarily responsible for originating the non-proliferation concept in 1958. He propelled the campaign with a heavy personal investment of time and energy in it. Although a senior and longstanding member of the Fianna Fáil government, closely aligned with the party’s elder statesman Eamon de Valera, his non-proliferation initiative was not immune from senior internal criticism. Seán MacEntee was another Fianna Fáil veteran and occupied the position of Tánaiste (deputy prime minister) from 1959. He formulated a cogent critique of Aiken’s non-dissemination designs in January 1961 that foreshadowed later criticisms of the NPT. MacEntee’s observations were pertinent to the constitutionalization of nuclear non-proliferation, and posed fundamental questions about national sovereignty, inequality, real politik, and implementation as Aiken entered his fourth year of advocacy for a treaty based on the Irish resolutions. Aiken had encountered such criticisms already and was relatively unperturbed. He overcame this divergent voice in the Cabinet to continue his efforts and persuade the incoming John F Kennedy Administration to support the drive for an NPT later that year.