This paper explores the prevalence and correlates of political incivility among Congressional candidates in the 2020 election cycle, focusing specifically on which types of candidates were most likely to use uncivil language in their online communications and the self-reinforcing nature of incivility between candidates. Based on a comprehensive analysis of more than two million tweets sent by major party candidates in the 2020 House and Senate races, we conclude that several individual and electoral factors were influential in driving candidate incivility. Specifically, Republicans, challengers, and candidates in less competitive races were more likely to use uncivil rhetoric. Women, racial minorities, and candidates running in open seat races were less prone to incivility. We also find that incivility begets incivility, with candidates whose opponents used higher rates of incivility also being more likely to use incivility themselves. Uncivil tweets were also found to generate significantly more likes and retweets, suggesting that incivility is a viable means of driving engagement for candidates. These results shed light on the factors behind incivility among political elites, as well as highlight the feedback effects which contribute to a self-reinforcing rise in political incivility.