"We are convening agencies to understand where the north Koreans are today. A lot has changed in the last four years. We are evaluating, diagnosing and talking about potential avenues, including engagement," the senior U.S. official said.The "closed-door discussions" involving think tank experts and current and former U.S. officials "suggest the Trump administration is sizing out different scenarios for another Trump-Kim meeting," said Andrew Yeo, a senior fellow at the Brookings Institution.