US Vice President Mike Pence has warned North Korea not to try to "play" Donald Trump, who is threatening to walk away from negotiations if the planned Singapore summit with Kim Jong-un fails.

Trump is due to meet South Korean leader Moon Jae-in in Washington to discuss the approach to the summit and the potential for denuclearisation.

Relations between North and South Korea looked like they had reached a turning point, only for things to become fractious again in the last week.

Has Trump been naive on this issue?

Cal Thomas and Marion McKeone discussed this and more from the United States.