Nevertheless, it cannot be concluded that there is certainly no difference between treaties and ex post-Congress executive agreements. Failure to reject the zero hypothesis differs from the evidence of the zero hypothesis. The number of ex post executive agreements in the sample is small. Therefore, the failure to reject the zero hypothesis may be due simply to large standard errors due to data scarcity. This is especially true for models (2) (5), which include a large number of covariates, resulting in data savings in many subgroups. The fact that almost all model specifications provide negative coefficients certainly allows a larger number of data to obtain a statistically significant difference, although a small one. 105 For example, HeinOnlines U.S. Treaty s. Treaty s Library provides access to the full text of a large number of international agreements. The president can reach an international agreement on any subject within his constitutional authority, as long as the agreement is not in contradiction with the legislation passed by Congress in the exercise of its constitutional authority. Among the constitutional sources of authority of the president to conclude international agreements are: for each agreement, the guide also mentions a “Senate contract number.” This number is assigned to any contract submitted to the Senate as part of the consultation and approval process.

Executive agreements do not receive a contract number from the Senate. The number can therefore be used to determine which agreement is a contract in the database and what agreement has been reached in the form of an executive agreement. Compare Bradford C. Clark, Domesticating Sole Executive Agreements, 93 Va. L. Rev. 1573, 1661 (2007) (arguing that the text and history of the Constitution support the position that treaties and executive agreements are not interchangeable, and also argue that the supreme clause should be read in order to avoid, in general, exclusive executive agreements being contrary to existing legislation); Laurence H. Tribe, Taking Text and Structure Seriously: Reflections on Free-Form Method in Constitutional Interpretation, 108 Harv. L. Rev.

1221, 1249-67 (1995) (on the grounds that the contractual clause is the exclusive means for Congress to approve important international agreements); John C. Yoo, Laws as Treaties?: The Constitutionality of Congressional-Executive Agreements, 99 L. Rev. 757, 852 (2001) (on the grounds that treaties are the constitutional form required for Congress to approve an international agreement on measures outside the constitutional competence of Congress, including human rights, political/military alliances and arms control, but are not necessary for agreements of measures under the powers of Congress.