Russia’s war on Ukraine is reshuffling Middle East diplomacy and forcing the U.S. to reassess the political costs of reviving the 2015 nuclear accord with Iran.

Clinching the deal after a year of negotiations now hangs on a sticking point that people familiar with the talks say has emerged as the most politically explosive for the administration of U.S. President Joe Biden — whether to remove Iran’s Islamic Revolutionary Guard Corps (IRGC) from the U.S. list of terrorist organizations.

The designation isn’t directly linked to the original pact, which curbed Tehran’s atomic activity in return for sanctions relief, but Iran has insisted all along that it be scrapped.