Twitter is an efficient conduit of information for millions of users around the world. Its ability to quickly spread information to a large number of people makes it an efficient way to shape information and, hence, shape public opinion. We study the tweeting behavior of Twitter propagandists, users who consistently express the same opinion or ideology, focusing on two online communities: the 2010 Nevada senate race and the 2011 debt-ceiling debate. We identify several extreme tweeting patterns that could characterize users who spread propaganda: (1) sending high volumes of tweets over short periods of time, (2) retweeting while publishing little original content, (3) quickly retweeting, and (4) colluding with other, seemingly unrelated, users to send duplicate or near-duplicate messages on the same topic simultaneously. These four features appear to distinguish tweeters who spread propaganda from other more neutral users and could serve as starting point for developing behavioral-based propaganda detection techniques for Twitter.