President Obama told incoming President Trump that North Korea would likely be the toughest item on his to-do list, and through the first 500 days of the administration, the prediction has proved correct. Kim Jong Un’s nuclear program has made regional allies, like South Korea and Japan, nervous, and heightened nuclear fears in the United States for the first time since the end of the Cold War. With all the drama over the on-again, off-again summit, where does the thorniest issue on Trump’s agenda go?