The high deliberative quality of political conversation among citizens is a valuable component when taking political decisions. However, online discussions often do not correspond to deliberative standards which can be found in the theory of deliberative democracy. In this paper, argumentation (reasoning) and communicative culture (civility and incivility) as the most relevant parameters of deliberation are analyzed in order to assess the quality of Russian and American social networks' deliberation. The research is based on a methodology of discourse analysis which allows to identify the deliberative quality of political discourse. The article presents the results of online discussions' analysis on significant issues in the Russian and American socio-political discourses - the court verdict of Alexei Navalny and the second impeachment of Donald Trump. As an empirical basis of study, online discussions on the pages of Vkontakte social network of four Russian media and discussions of four American media on Facebook are used. The authors conclude that social media deliberation as a form of public dialogue in Russia is poorly developed in terms of argumentation and culture of speech while American online deliberation is more developed, reasoned, polite and respectful.