The July 2015 deal was aimed at making it harder for Iran to make a nuclear bomb. At the time, it was believed Iran might be two to three months away from getting a nuclear bomb. But if Iran abided by restrictions imposed by the deal, it would take at least 12 months to build a weapon.
In exchange for curbing its nuclear program, Iran got access to tens of billions of dollars in assets (estimates are as high as $150 billion, but the exact amount is not known). But the vast majority of those assets were Iran’s own money, assets frozen as a result of sanctions imposed on Iran by the United States and other countries.
Clinton has said that her work as secretary of state in putting together sanctions against Iran helped usher Iran to the negotiating table. But Clinton was referring to work she did in 2009 and 2010. And she left the secretary position in February 2013. That means Clinton was gone for 2.5 years before the nuclear deal was struck. In other words, the heavy lifting was done under John Kerry, although Clinton endorsed it.
And President Barack Obama had to sign off on the deal, so it belongs to him more than any secretary of state.