Actually, Obama himself did not make the deal. That's the lie that Trump is telling. That deal was made by international cooperation with many countries. The Iranian nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), was a landmark 2015 agreement between Iran and the P5+1 (the US, UK, France, China, Russia, and Germany) designed to curb Iran's nuclear program in exchange for economic sanctions relief. At the time, Obama was President, but I bet the deal had to be approved by Congress. In any case, as soon as Trump got into power in his first term, he pulled the USA out of it.
That plan set a few end dates for the agreement and some of those dates came up in 2025. Therefore the plan is up for renegotiation. Because Trump pulled the USA out of the P5+1, the USA has no legitamate status in any future discussions.
Here is another link I found that will provide you with information about the JCPOA. https://www.cfr.org/backgrounders/what-iran-nuclear-deal