Sec State Kerry met twice with Oman’s foreign minister but could not reach a deal concerning Iran’s potentially weaponizable nuclear program.

Bill Clinton tried. So did George W. Bush. Neither succeeded. As President Barack Obama’s own second term winds down, he is getting closer than either of his immediate predecessors to the goal of improving U.S. relations with Iran. But he’s not there yet, and plenty stands in the way, including a messy and brutal conflict in Iraq and Syria.

Even as it prods Turkey to step up in the global fight against Islamic State militants, the United States is worried that Ankara might use military action to target Kurdish fighters who are the last line of defense against extremists trying to take over the Syrian border town of Kobani.