Members of the United States Congress are cross-pressured by constituents, party leaders, the president, and even by their own career goals. Yet, they are limited in their time and resources, and must maximise the tools available to them. Given that Congressional letter writing to the president as a tool available to all members occurs so widely, such behaviour informs a deeper understanding of how legislators seek to professionalise as politicians in competitive national politics. Utilising a data set of nearly 13,000 Congressional letters across eight Congresses, the author finds that letter writers systematically differ from non-letter writers, shedding light on the value of letter writing in Congressional behaviour and career aspirations, as well as the drivers behind this form of behaviour. Letter content varies based on the institutional and individual characteristics of the letter writer, suggesting members differ in how they view and use this tool.