Figure 3 shows that there is a 14% probability for an agreement at the end of the observation period, provided it is in effect by then. For executive agreements, this probability is 40%. Similarly, there is a 15 per cent probability that a contract will be broken between 1982 and 2012, while the probability is 50 per cent for executive agreements. 44 108 AJIL Unbound (2014), available from www.cambridge.org/core/journals/american-journal-of-international-law/ajil-unbound; See also Bradley, note 9 above, at 85 (accept with Hathaway that the different use of contracts and executive agreements does not reflect a recognizable logic). The view that treaties and agreements between Congress and the executive branch can be considered legal substitutes, of course, raises the question of why the United States needs two legal instruments to regulate the same types of international relations. Indeed, some commentators have asked why the United States should not abandon the treaty in favour of the agreement between Congress and the executive branch. Footnote 38 63 For example, it is difficult to compare a violation of a tax agreement with compliance with a nuclear weapons reduction treaty. See Simmons, Beth A., Treaty Collection and Violation, 13 Ann. Rev. pol. Sci. 273 (2010) for examples of fragmentation of contract compliance studies.
Table 2 presents a list of selected themes and the prevalence of contracts and executive agreements in each area. A full list of agreements by theme is included in the online appendix. The only subject on which treaties are more common than executive agreements is extradition, where 94% of agreements are concluded in the form of treaties. A likely explanation for this phenomenon is the uncertainty about the constitutionality of the use of executive agreements to give individuals to foreign nations. Uncertainty stems from Valentine v. United States, footnote 94, where the Supreme Court held that extraditions should be authorized “by Congress or by the terms of a contract.” Valentine did not consider whether the extradition complied with the Constitution in accordance with the executive agreement of Congress. Instead, the court considered whether the United States could extradite citizens without agreement or legislative power. As such, the reference to the “Congress file” could have been “purely dictated.” Note 95 Today, commentators are divided on whether extraditions can be authorized by an agreement between Congress and the executive branch, with some pointing to a lack of congressional authority over extradition and others interpreting Valentine as an explicit acceptance of such authority by the Supreme Court. Footnote 97 There are also other difficulties, perhaps deeper, with descriptive results.