  We introduce \emph{informational punishment} to the design of mechanisms that
compete with an exogenous status quo mechanism: Players can send garbled public
messages with some delay, and others cannot commit to ignoring them. Optimal
informational punishment ensures that full participation is without loss, even
if any single player can publicly enforce the status quo mechanism.
Informational punishment permits using a standard revelation principle, is
independent of the mechanism designer's objective, and operates exclusively off
the equilibrium path. It is robust to refinements and applies in
informed-principal settings. We provide conditions that make it robust to
opportunistic signal designers.
