 Emboldened by his success , Diệm began to plot Bảo Đại 's downfall . He scheduled a referendum for 23 October 1955 and pushed Bảo Đại out of the political scene , hindering the former emperor 's attempts to derail the poll . In the period leading up to the vote , campaigning for Bảo Đại was banned , while Diệm 's election campaign focused on personal attacks against Bảo Đại . These included pornographic cartoons of the head of state and unverified rumours claiming he was illegitimate and linking him to various mistresses . The government @-@ controlled media launched polemical attacks on Bảo Đại , and police went door @-@ to @-@ door , warning people of the consequences of failing to vote . After his brother Ngô Đình Nhu successfully rigged the poll , Diệm proclaimed himself president of the newly created Republic of Vietnam . 
