While the Trump administration is exploring strategies to thwart North Korea’s nuclear ambitions, former U.S. officials who dealt with the communist state extensively offer mixed views on how to achieve that goal. Earlier this week, Pyongyang launched four ballistic missiles in an apparent protest against U.S.-South Korea joint military exercises, prompting Beijing to intervene. Chinese Foreign Minister Wang Yi proposed Wednesday to halt the military drills in exchange for North Korea freezing nuclear and missile programs, a proposition that has been rejected by the United States and South Korea. Speaking to reporters after attending a U.N. Security Council meeting over the launches, U.S. ambassador to the United Nations, Nikki Haley, said the regime must take “positive action” before it can be taken seriously. She made her remarks a week before U.S. Secretary of State Rex Tillerson is scheduled to make his first trip to Asia, where North Korea is likely …