The rise to the US Presidency of Donald Trump has been accompanied by the emergence of a new political rhetoric, one that is most frequently observed on the social media platform Twitter. Although Twitter has been a feature of political campaigns and communication for several years now, the public has not been exposed to the deprofessionalised, informal use demonstrated by Trump. The rhetoric of Trump can be said in large part to be influenced by his personal history, and his persona as a celebrity TV star, especially through the informality, insults inclusive of nicknaming, and framing himself as a winner and opponents as losers. Although this new rhetorical style is present in all his discourse on Twitter, we focus this study on Trump's pursuit of legitimacy for his proposed border wall on the US-Mexico border, and do so from a Critical Discourse Analysis perspective by utilising Reyes' (2011) framework for legitimisation in political discourse. 1 INTRODUCTION Donald J. Trump's ascendency to the Presidency of the United States in 2016 heralded a new form of politician in conjunction with a new style of political rhetoric and communication. To understand Trump and his place within American and global politics, it is unwise to ignore his celebrity persona and background. King (2018, p. 2) states that where in the past 'politicians have sought to exploit the tropes and images of celebrity, the Trump Presidency marks the point where the President is a celebrity' (italics added). This is linked to both his past as a billionaire businessman, but most notably his role in the reality TV show The apprentice, which presented him with a kind of fame unique to reality TV show characters and different from the past, where 'fans are encouraged to feel that they know these people, not as fictional characters but as flesh and blood' (Von Drehle, 2016, p. 26). He has carried this fame and the influence of his celebrity into the political sphere, where the 'fact that he did not sound or behave like a typical politician won him points for authenticity' (Singer, 2016, p. 97), and this authenticity is evident in all of his political rhetoric, but particularly on his preferred mode of communication, the social media platform Twitter. Twitter has now been a prominent tool of political communication and participation for more than a decade, with politicians and political organisations engaging in what Maireder and Ausserhofer (2012, p. 306) describe as the