“The original deal was reached during Barack Obama’s presidency, after years of talks among Iran, the United States and other leading countries, including Russia and China. It lifted an array of nuclear sanctions on Iran in exchange for severe curbs on its atomic program. The deal had limits, however, including provisions that would expire over time, technically starting within the next three years. (Supporters of restoring the deal argue that the most important provisions won’t expire for several more years and some elements last in perpetuity.)”
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“the original Iran nuclear deal involves the Russians taking special roles in helping Iran implement the agreement, such as shipping out Iran’s excess enriched uranium. If Russia refuses to play that role, the deal is once again undermined.”
https://www.politico.com/news/2022/03/14/russia-biden-killing-iran-deal-00017113