Secretary of State John Kerry meets with Minister Mohammad Javad Zarif in Geneva, January 2015 (Martial Trezzini/AP) John Kerry meets with Iranian Foreign Minister Mohammad Javad Zarif in Geneva in January. (Martial Trezzini/AP)

The recent open letter from 47 senators to Tehran lecturing Iran’s leadership on the U.S. Constitution has attracted criticism for its judgment and even (rather less plausibly) its legality. We might pile on by noting its tone of broad condescension (“we hope this letter enriches your knowledge…”) and its tacit repudiation of term limits, once a Republican litmus test (“most of us will remain in office” for “perhaps decades.”)  As former Bush administration official Jack Goldsmith pointed out, the letter even got its exposition of the Constitution wrong. (Speaking of the Constitution, though, those accusing the senators of “treason” might want to read it.)

But the letter does serve as a useful reminder that treaties serve as a tiny fraction of international agreements. From the vantage of the White House, this makes perfect sense: Achieving a 2/3 vote authorizing ratification has become increasingly implausible no matter what treaty is under discussion. Recall that in 2012, even Bob Dole’s dramatic wheelchair-bound appearance on the Senate floor failed to convince his former colleagues to support the Bush-negotiated Convention on the Rights of Persons with Disabilities, which fell six votes short of the 67 needed.

Yet the trend far predates the current state of polarization, as Loch Johnson’s 1984 book on this topic makes clear.  A hugely useful Congressional Research Service report updated just last month notes that more than 18,500 executive agreements have been entered into since 1789: more than 17,000 of them from 1939 on. By the mid-1920s, the number of executive agreements had started to outpace the number of treaties, a trend vastly accelerated by World War II; between 1953 and 1972, more than three-quarters of significant military commitments abroad were conducted via executive agreement rather than by treaty.  These included, in the mid-1960s, major commitments to the defense of such nations as Ethiopia, Thailand and Spain. In the last case, the U.S. pledged to protect Spain (which did not join NATO until 1982) against attack in exchange for the right to use Spanish soil for military bases.

Legislative worries about secret and unaccountable American promises escalated during this time, goaded too by the Nixon-Kissinger penchant for back-channel diplomacy. Hearings in 1972 led to the Case-Zablocki Act, which required that “the text of any international agreement, other than a treaty” be submitted to Congress “as soon as practicable” but in any case within 60 days after the agreement took effect.  (See this State Department site for recent examples.)

Oral agreements were soon added to the mix, along with a requirement that presidents explain in writing any delays in reporting agreements to Congress. There were efforts to push even further — for instance, the proposed Treaty Powers Resolution would have prohibited presidents reaching “significant” agreements without seeking their ratification, prohibiting funding to implement any non-complying agreement, but “significant” proved too hard to define. Still, the cumulative debate did seem to have an impact: When the Spanish base agreement came up for renewal in 1975, the Ford administration submitted it as a treaty.

But even the Ford administration toyed with semantics, terming some “agreements” to be only “accords,” and presidential compliance with the Case-Zablocki reporting requirements has never been perfect. Certainly the making of executive agreements continued apace. Indeed, according to a 2007 study by political scientists Kiki Caruson and Victoria Farrar-Myers in Political Research Quarterly, between 1977 and 1996, presidents negotiated nearly 4,000 executive agreements but only 300 treaties, making agreements 92.9 percent of the whole. Some of these are routine, of course (e.g., legislatively-mandated fishery agreements), but many others are not. Recall that in 2008, lawmakers of both parties (including then-Sen. Joseph Biden) railed against the George W. Bush administration’s insistence that a long-term “status of forces agreement” dictating a continuing U.S. troop presence in Iraq could be approved administratively.  Glen Krutz and Jeffrey Peake, in their 2011 book “Treaty Politics and the Rise of Executive Agreements,” add many other consequential cases to the list.

So executive agreements are a fact of life. Nor are they “mere,” as the senators’ letter would have it. Nor, ditto, are they always easy to overturn (see U.S. v. Pink, for instance, as well as the more recent 1981 Supreme Court decision in Dames & Moore v. Regan, which upheld the complex executive agreement that ended the Iran hostage ordeal.) The CRS report referenced above does yeoman service in trying to unravel the legal standing of various forms of international agreements, and the various ways executive agreements can themselves rely on congressional support. Certainly executive agreements do have legal limits (as the CRS report notes, judiciously, “if … the President enters into an agreement and his constitutional authority over the agreement’s subject matter is unclear, a reviewing court may consider Congress’s position in determining whether the agreement is legitimate.”)  On the other hand, so far the sentiments expressed in the letter do not represent the codified will of the Congress, nor even the Senate.

In the end, the key limitation will be political: Foreign policy is always subject to domestic constraint. As Krutz and Peake note, executive agreements conducted in “truly unilateral fashion” without even tacit congressional cooperation will be “codified but essentially hollow.”  The difference between seeking a treaty and negotiating an executive agreement is, at base, a political question. So is the outcome of either.