This is what Trump did: (Not in chronological order.)

• First, he appeared unpredictable, radically different from the last 30 years of American leadership, and that alone was enough to scare North Korea. If you doubt this I challenge you to ask this question: Did you ever utter a phrase similar to “Trump as President is terrifying” or “Trump will lead us to World War III”? We all know your answers. If YOU were scared, most of you American, you should know damn well that the hermit kingdom that cannot match America’s power in any sense would be terrified.
• Second, Trump directly used harsh language, direct threats of FIRE & FURY, and directly lashed out at North Korea and KJU. Similar to the first point, this was so different and intimidating that it provoked North Korea into trying to display its strength on a regular basis. And eventually those shows-of-force failed. Failed to the point of the DPRK’s test site collapsing.
• Third, Trump closed sanction loopholes which made past sanctions hurt more.
• Fourth, Trump pressured China. China has long treated the DPRK like a bastard little brother, defending them reluctantly but ultimately only out of their own interests. China doesn’t rely on North Korea, in fact China’s trade with South Korea has been far more profitable, but China relies on there being a buffer zone between their borders and the United States (in addition to the previously stated fact China doesn’t want 25,000,000 refugees).

But who is China’s largest trading partner? The United States, of course.

So Trump threatened China: put pressure on North Korea or we will put pressure on you. China started by rejecting a coal shipment from North Korea. When China wasn’t helping enough, Trump called them out.

• Fifth, Trump created new sanctions and got China to join in. That first time was in September 2017. He issued another round in February 2018.
• Sixth, Trump demonstrated that even threats from big brother will not protect rogue states.
• Seventh, Trump committed to a dramatic show of force, that unlike the DPRK’s, didn’t fizzle out.

President Trump did not single-handedly bring Kim Jong Un to the negotiating table, but he sure as hell was the primary motivator. President Xi and President Moon deserve credit too. Hell, even Kim Jong-Un, for the criminal he is, deserves credit for bringing his country to the table. We may not even get peace or denuclearization, as much as that sucks to acknowledge, but the fact we are even having this discussion outside of a thought experiment is something President Trump, and the others, deserves credit for.