Twenty days ahead of a summit with Democratic People's Republic of Korea's leader Kim Jong-un planned for June 12, US President Donald Trump said on Tuesday it might not happen. "There's a very substantial chance it won't work out," Trump said when he was asked about the conditions for meeting with Kim. "That doesn't mean it won't work out over a period of time," Trump continued. It was the first time Trump raised doubts about the Singapore summit so explicitly. "It has a chance to be a great, great meeting for North Korea and a great meeting for the world," Trump said on Tuesday.