Trump should be quiet. The reality is that Trump’s sanctions are working, and will really put the screws to NK. NK feels if they can make Trump turn it into a defense issue then they can wriggle out of it, or get China to support them. But as long as the sanctions have a chance these guys will fold.
I think that Trump, by not being 'quiet', is the motivation for the sanctions to have an effect. Who can predict what either leader will do. The entire world now has a stake in this matter. Prior administrations didn't want to deal with this nut and it is now Trumps duty to defend our country against all threats.
Trump has had the courtesy to learn the language of his enemy. It has proven to be an effective tool.