The growth of Twitter has forever (or at least until some other new Internet revolution comes along) changed the way politicians and political groups interact with their supporters. Keeping in touch with constituents or organizing a populist lynch mob has never been easier. But the format of Twitter, which encourages quick, timely bursts of thought, can also backfire on people who generally have to be very careful about what they say and how they come across to the world. Which is to say, every so often, these tweets can go horribly awry. In fact, there has emerged a special class of tweets that are so embarrassing, in some form or another, that their authors deleted them entirely after posting, hoping to strike them from the public record. Except, of course, that it’s close to impossible for something to ever really be deleted once it’s on the Internet. To help politicians avoid such disasters in the future, let’s take a look at these tweets, and the lessons they can teach us.