Bujor rallied with the Poporanist movement, infiltrating the National Liberal Party from the left. He was among the founders of the leading Poporanist review, "Viața Românească", but expelled after expressing disagreement with its refusal to criticize the National Liberal mainstream. As an independent left-winger, constantly pushing for land reform and universal suffrage, Bujor had publicized and sometimes violent conflicts with his far-right colleague at university, A. C. Cuza. Elected to Senate as a university representative, and serving throughout the social upheaval of World War I, Bujor clashed with the National Liberal Prime Minister Ion I. C. Brătianu, whom he accused of bringing disaster upon the country. In 1919, he was one of the founders and leaders of Peasants' Party, which became part of a successful electoral coalition, representing groups throughout Greater Romania; Bujor was selected as Greater Romania's first president of the Senate.