The latest back-and-forth on a nuclear deal between the United States and Iran hinges on enrichment, and the question may put nails in the coffin of any new agreement. White House envoy Steve Witkoff said Sunday , after weeks of mixed messages, that no future accord can allow Iran the right to enrich uranium. "We have one very, very clear red line, and that is enrichment," Witkoff told ABC This Week ’s Jonathan Karl. "We cannot allow even 1 percent of an enrichment capability." Iranian supreme