BERLIN—U.S. and European officials are increasingly gloomy about the prospects of reviving the 2015 nuclear deal with Iran before the U.S. midterm elections, as a hardening of demands from Tehran raises doubts about its willingness to conclude a deal soon.
U.S. officials say no decision has been taken by the administration to shelve the diplomatic effort, but a tightening political calendar at home leaves little time to reach a final agreement.