WASHINGTON — They have spent long hours alone together. They exchange private emails. Their walk along the Rhone River in Geneva in January so unnerved hard-line lawmakers in Tehran that they signed a petition fretting about the duo’s unseemly “intimacy.” On Sunday, Secretary of State John Kerry flew to Switzerland to meet again with Mohammad Javad Zarif, the Iranian foreign minister who earned a Ph.D in international law and policy from the University of Denver, to try to negotiate the very accord that Prime Minister Benjamin Netanyahu of Israel arrived in Washington that same day to denounce. As the deadline approaches for what could be one of the most important and divisive international agreements in decades, Mr. Kerry has become a driving force behind the complicated, seven-nation talks to limit Iran ’s nuclear program . But with so much at stake, Mr. Kerry’s relentless negotiating style and determination to […]