Why I think so:
First, while it's easy to discount Trump's outbursts, his "fire and fury and frankly power" "if [North Korea] does not stop threatening the United States"* statement yesterday is coupled with the leaking of "intelligence" -- actually preparatory propaganda -- intended to justify just that. From the WaPo story linked above:
Trump's statement also followed a report in The Washington Post that North Korea has successfully produced a miniaturized nuclear warhead that can fit inside its ballistic missiles, crossing a key threshold on the path to becoming a full-fledged nuclear power. The report quoted a confidential assessment by U.S. intelligence officials.
In actuality, 1) North Korea still seems to be at the stage of producing bulky fission weapons; 2) the recent claims (from both Pyongyang and DC) that the North has developed an ICBM capable of reaching US targets seem pretty sketchy; and 3) even if the North has produced real nukes (fusion weapons) and even if the North does now theoretically have the capacity to hit the US with missiles, miniaturizing those hypothetical nukes and mating them with those hypothetical missiles and expecting them to detonate at the far end of an arc taking them to the edge of space is another giant leap.
Secondly, I've previously predicted that in the event of such a conflict, the Chinese regime will be tuned up and ready for an invitation from the North's military to intervene as "peacekeepers" after a brief US air war and the collapse of the Kim regime. They seem to be rattling sabers as prelude to such a scheme.
As I've previously predicted, I don't think a US ground invasion of the North is part of the plan. For one thing, that would take a major, highly visible, time-consuming ramp-up. The North would likely decide to kick things off themselves long before the US gets its ginormous mass of troops, tanks, etc. landed and in position.
What US ground combat there is will take place along the 38th parallel "demilitarized zone" (which of course means the opposite of what its name implies). That will get ugly, and there will be casualties, but I don't expect the North to be able to wreck, let alone occupy, Seoul as some people like to predict -- some artillery/rocket fire at extreme range in the first hours, trailing off as the North's guns are turned into twisted piles of metal by US air and artillery, if they don't run out of ammunition first (resupply won't be happening).
The US, from the air, will first of all destroy any and all ballistic missile and/or atomic sites it knows of (and it knows of most, if not all, of them), followed by C3I (Command, Control, Communications and Intelligence) targets and road/transportation targets. The first objective will be to make it impossible for the North's military to function as an offensive force at the DMZ or outside the Korean peninsula. The second will be to make the North's military come apart at the seams in general. And the third will be to ensure that the Kim regime loses any ability to direct its military forces, presumably culminating in one or more generals deciding that it's time to march Kim Jong Un and friends around back for a bullet party right before asking Beijing to come in and restore order.
Obviously, the more detailed predictions above are more risky than the one in the first sentence. But I think it's coming soon, and I do think that's how it will go ... now let's see whether or not I'm right so I can either crow or eat crow (frankly I'd much rather do the latter on this one).
* It's worth noting the content of the "threats" Trump cites as reason for his own threats. To wit (WaPo op. cit.):
North Korean Foreign Minister Ri Yong Ho told diplomats that his country will never negotiate away what he called a rational "strategic option" against the threat of attack from the United States.
Bombast notwithstanding, the North's "threat" is that it will defend itself if attacked and that it will build and maintain a nuclear arsenal as a deterrent to attack.