Substantial changes in policy are sometimes implemented by "unlikely" parties; for example, radical market-oriented reforms by populist parties and substantial steps towards peace by "hawks" like Begin or Nixon. To account for such episodes, we develop a framework in which incumbent politicians have more information than the voting public about the state of the world, and hence about which policies are optimal. Politicians are unable to transmit fully this information, since there is also incomplete information about their preferences. We conclude that popular support for a policy, or its "credibility," depends on the policymakerpolicy pair.