NEW: Trump admin received information that Kim Jong Un had heart surgery last week and if he& #39;s alive, his health is poor, I& #39;m told. KJU hasn& #39;t been seen at key events in recent days. It& #39;s unclear to US officials if he& #39;s dead or alive. (CNN 1st reported his condition& #39;s grave.)

Trump administration officials are looking into who would be in the line of succession if Kim Jong Un dies or is already dead, I& #39;m told.