Does money in politics affect democratic performance? I study the effect of the Supreme Court's 2010 landmark decision in Citizens United v. FEC, which struck down existing state bans on independent campaign expenditures, on democracy in the U.S. states. Results from a difference-in-differences design indicate that the Citizens United ruling had a substantial negative effect on state democratic performance and that this effect is largely independent of the effect of Republican party control identified by previous research. The results suggest that unlimited political spending may pose a threat to the health of democracy in the United States.