Listen to the Market, Hear the Best Policy Decision, but Don't Always Choose it

Real-world policymakers want to extract investors private information about a policy's likely effects by listening to "asset markets". However, this brings the risk that investors will profitably "manipulate" prices to steer policy. We model the interaction between a policymaker and an informed (profit-seeking) investor who can buy/short-sell an asset from uniformed traders. We characterize when the investor's incentives do not align with the policymaker's, implying that to induce truth-telling behaviour the policymaker must commit to sometimes ignoring the signal (as revealed by the investor's behaviour driving the asset's price). This implies a commitment to executing the policy with a probability depending on the asset's price. We develop a taxonomy for the full set relationships between private signals, asset values, and policymaker welfare, characterizing the optimal indirect mechanism for each case. We find that where the policymaker is ex-ante indifferent, she commits to sometimes/never executing after a <em>bad</em> signal, but always executes after a <em>good</em> signal. Generically, this "listeneing" mechanism leads to higher (policymaker) welfare then ignoring the signals. We discuss real-world evidence, implications for legislative processes, and phenomena such as "trial balloons" and "committing political capital".