Re: He thinks it will be a "legacy" of his.
You're half right: Obama does see this as a big part of his legacy. Although why he would focus on Iran's nuclear program rather than some other foreign policy issue like normalizing relations with Cuba or defeating ISIS or rolling back Russia in Ukraine or even leaving Afghanistan better than he found it, I don't know.
As for the stuff about him not caring about the safety of the country or the world? That's just ignorant, and I don't know why anyone would say that about any president.