"We are not going to sit at the negotiating table forever. We also recognize that we shouldn't get up and leave simply because the clock strikes midnight," Kerry said from Vienna, where the talks are taking place.  The deal's deadline has been extended twice, and both U.S. and Iranian officials have said differences remain ahead of a third deadline on Friday.  In an interview with CNN's Christiane Amanpour, E.U. Foreign Policy Chief Federica Mogherini said "the moment of truth will come extremely soon, (in the) next hours I think."  In his comments Thursday, Kerry stressed that despite the tough issues that still have to be resolved, progress continues to be made.  "Let me assure you we would not be here continuing to negotiate just for the sake of negotiating," Kerry said. "We're here because we believe we're making real progress toward a comprehensive deal," Kerry said.  Iranian Foreign Minister Mohammad Javad Zarif on Thursday also addressed journalists, who questioned how long he would stay.  "As long as necessary," Zarif replied.  READ: Obama: Chances of an Iran nuclear deal now lower than 50-50  Delaware Sen. Chris Coons, a Democrat on the Foreign Relations Committee, interpreted Kerry's words Thursday as "a determination to send a message to the Iranian supreme leader that the deal that's on the table is the best deal you're going to get -- you either need to accept it or we're going to walk away."  Coons, speaking to CNN's Brianna Keilar, said that he was encouraged by Kerry's remarks.  "I do think there will come a point here soon where we should walk away if the Iranians don't agree," Coons said.  Senators on both sides of the aisle said they preferred that the U.S. delegation takes its time in the negotiations rather than rush to get a deal.  "I would much rather they take time on the remaining issues and make sure they do the very best they can to get them as good as they can," said Tennessee Republican Sen. Bob Corker, chairman of the Foreign Relations Committee. "I'd rather they delay than end up in making what's been a very downward trend the last couple of months even more downwardly trending."  Sen. Ben Cardin, a Maryland Democrat, told CNN that he "was not surprised" by the extension of the deal's deadline.  "We here are not anxious. We want him to take as much time as he needs. Within reason," he said.  Kerry's statement comes two days after President Barack Obama held a closed-door meeting with Senate Democrats in which he lowered expectations that a deal would be reached.  Senior Democratic Sen. Dick Durbin of Illinois said the President told the group that the chances of a nuclear agreement coming together were "below 50-50."
Secretary of State John Kerry made it very clear that he is not afraid to walk away from the Iranian nuclear deal currently in the works.