Following the Nuclear Security Summit in March 2016, U.S. president Obama says world leaders had expressed concern about Mr. Trump's comments in private conversations with him. Obama said- "even those countries that are used to a carnival atmosphere in their own politics want sobriety and clarity when it comes to U.S. elections because they understand that the president of the United States needs to know what's going on around the world." Obama said that comments by Mr. Trump showed a person "who doesn't know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally. Mr. Trump said in a NYT interview that "Now, wouldn't you in a certain sense have Japan have nuclear weapons when North Korea has nuclear weapons?" Trump has defended these comments in a televised townhall meeting held by CNN in Milwaukee. Obama was critical of these comments as upsetting the situation in Asia where the U.S. has made great sacrifices in World War II, and today "underwrites the peace and prosperity of that region." Adding that "you don't mess with that."...