In his oft-cited Prague speech of 2009, Barack Obama announced “a new international effort to secure all vulnerable nuclear material around the world within four years.” The effort’s highest-profile element was a series of Nuclear Security Summits that began in Washington in 2010 and concludes, again in Washington, in 2016. Clearly the initiative hasn’t “secure[d] all vulnerable nuclear material,” much less done so within four years. But that isn’t necessarily to say that the effort has failed—or that it shouldn’t be perpetuated. Below, experts from Ghana, Turkey, and the United States debate how much the Nuclear Security Summits have accomplished; what still must be achieved to ensure the security of nuclear materials worldwide; and whether, after the final scheduled summit, the international community should seek to continue the process.