In February 2022, Russia invaded Ukraine. The Putin regime used extensive and aggressive propaganda to win public support for the war. But can this propaganda really convince ordinary people? Using the unique timing of a survey experiment fielded a year before the invasion, we provide the first experimental evidence of the effectiveness of this propaganda among Russian citizens. Vignette treatments containing information on threats similar to stories running in Russian media around the time of the invasion in combination with statements from President Putin show that propaganda was highly effective. Even mild treatments were enough to increase support for military aggression against neighboring countries among Russians from around 8 to 48% and up to 59% among Putin's supporters. Thus, the Russian president had good reason to believe that he could control popular opinion when he decided to launch a war against Ukraine.