Secretary of State John Kerry on Thursday said that negotiators were still grappling with difficult issues in the talks on limiting Iran ’s nuclear program , but that they had made some headway. “We are pushing some tough issues, but we made progress,” Mr. Kerry told reporters in Lausanne during a break in the talks. It was not yet clear, Mr. Kerry said, whether the United States team would return to Washington on Friday or remain here through the weekend to continue negotiating with the Iranians. Iranian officials have spoken optimistically about the chances for sealing an accord in the coming days. The Iranian statements may be intended to build public pressure on the United States and its allies to make concessions, as well as to strike a positive tone for the Iranian public. But the United States and some of its European negotiating partners have […]