In Washington Post v. McManus, the Fourth Circuit invalidated a Maryland law that created disclosure-and-recordkeeping duties for online political ads. According to the court, Maryland’s law violated the First Amendment because it placed these disclosure obligations on the platforms hosting the ads rather than the political actors buying the ads. This risked “manipulating the marketplace of ideas.”

The McManus decision joins a long and unfortunate line of cases that rely upon a vague and functionally meaningless account of the “marketplace of ideas” to invalidate campaign finance regulations. These cases strike down laws for “interfering” with the marketplace of ideas without first explaining what the marketplace of ideas is or exploring how such a market might actually operate.

In this Article, I evaluate online-platform disclosure laws under a thicker conception of the marketplace of ideas using the attentional-choice theory of competition. Contrary to the outcome in McManus, I conclude that platform disclosure laws are fully consistent with (and even supportive of) robust competition in the marketplace of ideas.