Mass public opinion has generally been presumed to have little or no impact on American trade policy. I argue against this presumption. I assert that mass public opinion significantly affects US trade policy by shaping the way the two parties compete over that trade policy. When public opinion is unbalanced, the competition between the parties is likely to resemble a bidding war. When public opinion is balanced but split in a partisan manner the competition is likely to descend into Manichean conflict. When public opinion is balanced but split in a non‐partisan manner, the competition is likely to be characterised by political actors seeking to maintain the support of their core constituencies. To examine this relationship, I investigate three cases: the push to punish China over Tiananmen Square in 1989–90, the ratification of NAFTA in 1992–93 and the process through which President Bush was granted trade promotion authority in 2001–02.