Afghan presidential candidate Ashraf Ghani Ahmadzai, center, arrives to addresses a news conference in Kabul, Afghanistan, Thursday, May 15, 2014. Afghan voters will return to the polls next month to choose a successor to outgoing President Hamid Karzai, whose refusal to sign a deal permitting U.S. troops to stay beyond the end of the year has raised security concerns as the Taliban press their deadly campaign of bombings and attacks. (AP Photo/Massoud Hossaini)