In what may well be the most NORK-y Fourth of July fireworks display ever, the Pyongyang regime appears to have successfully tested a nuclear-capable missile with the range to reach the western portions of North America; by definition an intercontinental ballistic missile.
The linked article does a good job discussing the strategic implications of this success, but the tl:dr version is "there are no good military options".
Simply put, the DPRK appears to have obtained what Stalin's Soviet Union did in the 1940s; a successful defense against U.S. military strongarming. Never a particularly good idea, given the NORK capabilities for inflicting nasty mayhem to American-aligned nations in northeast Asia, if the NORKs have the capability to directly threaten the U.S. mainland this option goes from "barely conceivable" to "off the table".
What's more, the strategic calculus of potentially-holding-U.S.-population-centers-hostage changes the relationship between the U.S. and Asian allies such as Japan and South Korea. If Trump wanted the Japanese government to start building its own nukes Pyongyang may well have given it the same push that the Soviets gave the British and French governments during the Cold War - the worry that the Land of the Big PX would be hesitant to risk its own civilians in the face of a possible nuclear exchange.
Where does the Tangerine Toddler fit into all this? Swinging the Big Stupid bat, of course. The King of the Deal is discovering what diplomats and potentates throughout history have discovered, albeit at his own, short-bus-slow-reader speed; that polities with interests that conflict with your own can't always - and often won't ever - be coaxed, swayed, or bullied into acting against their own interests. China fears a NORK collapse more than anything the U.S. can threaten. Figuring out a way to adjust U.S. geopolitical approaches to the new northeast Asian realities will require a hell of a lot more patience, creativity, and intelligence than either the current Chief Executive - who seems more interested in ginning up a "Blut und Ehre" white nationalist agenda - or his people have shown to date.
Nukes are funny things. Technically they are "weapons of war"...but they work well only as potential, not kinetic, energy. When the first nuke is thrown at a nuclear-armed adversary they have effectively lost much of their usefulness. If war is the "continuation of politics by other means" the problem with nuclear war is that, unlike politics, there is no real way to plan or predict or strategize what happens after the fallout settles. A single warhead getting through to a single city will mean that even the "winner" will suffer. There is little consolation for the "winning" public knowing that the northern portion of the Korean peninsula is a glassy wasteland.
Maintaining the nuclear balance was a difficult task for U.S. leaders like Truman and Eisenhower. What happens when the launch codes are clutched in the stubby fingers of a man whose primary education in conflict was as a WWF wrestling heel is something that I'm not sure I want to find out.
Update 8:30am: And speaking of the Hermit Kingdom, this little piece is intriguing in its' suggestion that the NORKs may present a "World War Z"-type problem, too; the primitive medical capabilities of the Pyongyang regime offers terrific possibilities for the incubation and spread of nasty epidemic diseases. North Korea! It's like a Disneyland of Death!