The head of Iran’s nuclear agency said Monday that the landmark 2015 deal between Tehran and world powers on his country’s atomic program is struggling since the unilateral U.S. withdrawal, but is still worth preserving. Ali Akbar Salehi told delegates at a conference of the International Atomic Energy Agency in Vienna that the so-called Joint Comprehensive Plan of Action, or JCPOA, has been “caught in a quasi-stalemate situation” since President Donald Trump pulled the U.S. out in 2018. The remaining world powers in the deal — France, Germany, Britain, China and Russia — have been struggling to offset re-imposed American sanctions.