In tough diplomacy, the world came together to prevent Iran from getting a nuke. Even Israeli intelligence said Iran was in compliance. Trump blew all that up by leaving the agreement unilaterally, claiming he could get a better deal. Instead, he gave us war.
The Obama-Iran deal set back Iranian nuclear development by over a decade, and was intended to be the start of negotiations and the relationship, not the final say. They hoped the next president, Hillary Clinton, could push deals forward. Instead, Trump was elected and took a different path.