Trump did nothing of the such. Trump canceled a pre-planned training exercise with South Korea. I assume that is a move, by Trump, to prove his seriousness in achieving an agreement with Kim Jun Un. Kim Jung Un has released the 3 Americans that were being held and they are now back in America, this was achieved by the Summit even though it happened before. North Korea suspended their testing and test that flew missiles over Japan. North Korea has also met with South Korean leader twice and agreed to help the US repatriate bodies of many of those killed in the Korean War. Trump also achieved an actual face to face meeting with the North Korean leader where the two shook hands and agreed to future meetings (one in Washington and one in the North Korean capital) as well as total abanding of North Korea's Nuclear program. Although that has not happened and is only a promise it's far more than ever achieved before. That's not to mention the cessation of propaganda broadcast that was constantly happening through the years across the border nor the elimination of at least three, if not more, of HARDCORE North Korean military leaders that would have surely argued against any kind of agreement or peace with the United States or South Korea. Kim Jung Un has purged his military of many of these hard liners which also is a real sign that he is potentially ready to deal.
The US is still in the area of the South China Sea and there is still a conflict with China over that area but the move to cancel the planned exercises is a very demonstratable sign that the US, and Trump, are serious about working to get a working agreement. The real breakthrough will be when/if North Korea reveals the location and numbers of their nuclear arsenal, testing sights, and locations of the material to make the weapons. That is yet to come and would be a more visible demonstration of Kim's seriousness at disarming.
Either way, giving far more promise of a real agreement that has existed in the last 50 to 60 years. There is a real chance of seeing the reunification of the Korean peninsula and an official end to the Korean war and potential development in the North.
I know it's very difficult for the folks that hate Trump and Republicans to see these things happening under Trump and seeing him do yet another thing to completely demonstrate how insufficient and inept that Obama was, as President. Trump achieved this without the removal of any of the sanctions that exist, that brought N. Korea to the table as well as happening without a plane full of cash being flown to an N. Korean airport like Obama gave to the Mullahs of Iran in order to get the Americans that Iran held released. The Three Americans were released before the summit was ever conducted as a sign of good faith, just like the cancellation of the pre-planned military exercises is a demonstration and sign of "good faith" and demonstration of trust in Kim Jung Un's word.
I admit things could still fall apart (as so many Democrats and Trump opponents hope and pray it will) but we've (the United States and the World) never been at such an optimistic place with North Korea. Contrast what has been happening in North Korea to the Iran agreement where Iran gave up nothing at all and received such a huge cash payment, releasing of sanctions and cash that had been held. The agreement with Iran also never had to be signed by Iran's governmental leaders and also did not keep them from achieving Nuclear weapons but guaranteed it within 10 years as well as providing protection, from the United States, from possible attacks from Israel (our best Middle East Friend). Trump totallly outshined Obama in every way.