Big picture view:
Beyond the immediate walkout, several sticking points threaten to derail the peace process:
Uranium Enrichment: Iran’s President stated his nation will never surrender the right to enrich uranium, insisting the U.S. will be forced to accept it. Trump has repeatedly stated Iran cannot be allowed to develop nuclear weapons.
The Conflict in Lebanon: Iran is demanding Israel halt attacks on its proxies in Lebanon before U.S. talks resume. Israel, which is not participating in the Switzerland summit, says it will keep forces in Lebanon as long as necessary to protect Israelis.