When antagonist countries are at odds on everything else, swapping prisoners can be a low-cost way of easing tension while scoring small successes for the respective leaders. Iran and the United States managed one such win-win prisoner swap in early December. Arrangements are largely worked out for another, but will require both sides to take yes for an answer. 

On Dec. 7, Princeton doctoral student Xiyue Wang was released from his 3-year-long imprisonment in Iran in exchange for the US release of Iranian stem-cell scientist Masoud Soleimani. The latter had been arrested for a failing to obtain the required licenses to export human growth products for medical research, a minor violation of sanctions regulations.

Three elements made the December swap possible. Firstly, both sides had to be convinced that it was in their interest. For the United States, this should be a no-brainer. President Donald Trump has placed a high priority on winning the freedom of Americans imprisoned abroad, and he is quick to boast of those who have come back on his watch, especially if can contrast it, however incorrectly, with the record of his predecessor, Barack Obama. In this case, the Trump administration was able to boast that no cash was involved in the exchange.

Trump and his allies contrasted the moneyless Wang-Soleimani swap with the $1.5 billion in cash transferred to Iran in January 2016 coinciding with the implementation of the Iran nuclear deal and the release of Washington Post reporter Jason Rezaian and four other dual US-Iranian nationals in January 2016. Those five were released in exchange for the US dropping charges against seven Iranians, mostly dual nationals, arrested for sanctions violations. The cash transfer was the settlement of a three-decade-long financial dispute in which Iran received its own money back plus a small fraction of the accrued interest.