Information sets, expectations, and preferences of politicians are fundamental, but unobserved determinants of their policy choices. Employing repeated votes in the US House of Representatives on China's normal trade relations (NTR) status during the two decades straddling China's World Trade Organization (WTO) accession, we apply a moment inequality approach designed to deliver consistent estimates under weak informational assumptions on the information sets of members of Congress. This methodology offers a robust way to test hypotheses about what information politicians have at the time of their decision and to estimate the weight that constituents, ideology, and other factors have in policy making and voting. (JEL D72, D78, D83, D84, F14, P33)