Trump on Twitter tirade

President Donald Trump is exchanging schools yard taunts with North Korea's Kim Jong-un.   

Trump says in a tweet from Vietnam: ``Why would Kim Jong-un insult me by calling me ''old,`` when I would NEVER call him ''short and fat?``''  

Trump goes on to say sarcastically, ``Oh well, I try so hard to be his friend'' and says that, ``maybe someday that will happen!''  

Trump has been working to rally global pressure against North Korea's nuclear weapons program on a trip to Asia. That includes a stern speech delivered in South Korea. 

Kim's government responded to that speech by calling Trump an ``old lunatic.''