I have so far treated each country's executive as the sole decision maker for trade policy. In the theory, a single actor chooses trade policy to maximize political support. This theory is parsimonious and potentially powerful, but clearly incomplete. In particular, this approach leaves out legislatures, which normally hold or share responsibility for a country's autonomous tariff. As we saw in Chapter 8, high autonomous tariffs make trade cooperation less likely, whereas low autonomous tariffs have the reverse effect. Because of their autonomous tariff-setting authority it is important to examine the legislature's role in trade cooperation.

A country's legislature may also have the ability to veto trade treaties. When treaties require legislative ratification, executives may find it harder to liberalize tariffs through international agreement. A growing literature argues that such domestic ratification institutions, combined with differences between executive and legislative preferences, explain both the tariffs chosen by the legislature and the trade agreements negotiated by the executive (Lohmann and O'Halloran 1994; Mansfield et al. 2000, 2002a; Milner 1997a; Milner and Rosendorff 1996, 1997; but Pahre 2001a).

This chapter first examines the role of ratification institutions indirectly, by looking at the set of treaties rejected by domestic legislatures. This analysis shows that legislatures mattered for a small number of countries.