Does external monitoring improve democratic performance? Fact-checking has come to play an increasingly important role in political coverage in the United States, but research suggests it may be ineffective at reducing public misperceptions about controversial issues. However, fact-checking might instead help improve political discourse by increasing the reputational costs or risks of spreading misinformation for political elites. To evaluate this deterrent hypothesis, we conducted a field experiment in nine U.S. states in which a randomly assigned group of state legislators were sent a series of letters about the risks to their reputation and electoral security if they are caught making questionable statements. The legislators who were sent these letters were substantially less likely to receive a negative fact-checking rating or to have their accuracy questioned publicly, suggesting that the threat posed by fact-checking can reduce inaccuracy in statements made by political elites.Funding support was provided by the Democracy Fund and New America Foundation. We thank Kevin Esterling, Tom Glaisyer, Michael Herron, Donald P. Green, and audiences at Duke University and Dartmouth College for helpful comments. We are also grateful to Eric Yang and Eli Derrow for excellent research assistance.