How many treaties ratified by Congress did the US exit unilaterally?

Question

In an attempt to better focus a recent question asked here that is popular but very open to interpretation (which alas often happens on politics SE), I want to ask:

Are there any statistics on international treaties ratified by the US Congress but then exited by the US unilaterally, either through:

• Congress abolishing the treaty, or
• the Executive invoking a clause in the treaty that allows the Executive by itself to exit the US from the treaty (which entails that Congress pre-approved/delegated this method of exit to the Executive)?

Note that the latter seems not an uncommon case, e.g. Trump threatened South Korea with doing just that in order to get them to renegotiate [a new] KORUS treaty:

Late last week, the White House began preparing the documents to officially notify Korea under Section 24.5 to provide a six month notice that the U.S. wishes to terminate KORUS. Key Congressional leaders have been notified that this termination could be transmitted as early as Monday. [...] If the President does invoke Article 24.5, and no further action is taken, KORUS will terminate 180 days after such notice is given.

Ultimately that didn't happen and S. Korea renegotiated KORUS, but my point here is that while Congress is needed for ratification, it does not seem needed for the exit if Congress pre-approved/delegated the exit procedure for a treaty... as part of the treaty.

A futher background article even says:

although it took a 1945 vote in the Senate to allow President Harry Truman to ratify the U.N. Charter, the current weight of legal opinion holds that President Donald Trump has the power to withdraw the U.S. from this or any treaty without similar consultation with the legislative branch of government.

Since this question is probably going to be hard to answer from primary sources due to the volume of work that would be involved, I assume whatever analysis is cited in an answer is going to set its own criteria for "unilateral exit". With my elaboration above, I just wanted to prevent a simple/incorrect answer that would only count treaties explicitly abolished by Congress.

So, to reiterate the question (paying attention procedural issues mentioned above): how many treaties ratified by Congress has the US then unilaterally exited?

Answer 1

As noted in the question, this doesn't happen very often. Applying statistics to rare events can be highly misleading. If any statistics are available, they will probably lack statistical significance.

However, in 2001, the congressional research service published Withdrawal from the ABM Treaty: Legal Considerations. It doesn't offer a statistic, but examines in detail relevant examples, statutes, and case law. It has sufficient detail to distinguish between categories you mention.

Particularly relevant to the point you seem interested in is the exclusive presidential authority to suspend (rather than withdraw from) a ratified treaty. The report confirms that, from a practical standpoint, suspending the INF treaty does not require legislative approval.

While acknowledging that the Constitution does not expressly authorize the President to suspend an international agreement on behalf of the United States, the Restatement (Third) concludes that he may do so because he is empowered to conduct the foreign relations of the United States. The Restatement’s rules covering suspension are formulated accordingly. Thus Section 339 provides that:

Under the law of the United States, the President has the power (a) to suspend an agreement in accordance with its terms; (b) to make the determination that would justify the United States in suspending an agreement because of its violation by another party or because of supervening events, and to proceed to suspend the agreement on behalf of the United States; or (c) to elect in a particular case not to suspend or terminate an agreement.

… Under his authority to conduct the foreign relations of the United States, the President makes the determination that justifies suspending an agreement because of a material breach by another party. Accordingly, as a practical matter the President has the power to suspend a treaty since the courts look to executive determinations for guidance respecting the continued viability of a treaty.

[internal citations omitted]