How do authoritarian regimes make propaganda persuasive? This study theorizes and tests the effectiveness of foreign intermediaries or ``useful idiots" in propaganda messaging. Despite the commonality of foreign intermediaries in Chinese, Russian, or Iranian state media, the impact of these foreign intermediaries on audiences remains unclear. We conducted two survey experiments with approximately 4,800 respondents in mainland China and the United States, randomly exposing participants to soft propaganda videos featuring either American or Chinese speakers discussing positively the extent of freedom and safety they feel exists in China and praising its political model. Our findings show that foreign advocates do not enhance the effectiveness of authoritarian propaganda among Chinese audiences. However, Americans are more influenced by propaganda messages delivered by a fellow American than by a Chinese messenger. This demonstrates that ``useful idiots” are effective at improving perceptions of authoritarian rule among Western but not domestic Chinese audiences. Our findings show how autocracies can build global support through foreign intermediaries which, given currently heightened geopolitical competition, has implications for democratic resilience.