Kim's rocket scientists have been clearly working on developing their technology, testing engines and firing missiles at a steady pace, raising suspicions that they are working on the separate stages of an ICBM.
Yesterday, North Korea launched yet another medium-range ballistic missile, apparently testing a new land-based version of its submarine missile. Analysts fear these tests are part of a broader ICBM programme as they could form separate stages of a three-stage long-range missile.
But will the developers be able to put them all together and fire it? Will they be able to mount a nuclear warhead on that missile? How much of a threat does this pose to Americans? What can the Trump Administration do to stop North Korea?
Does North Korea have an intercontinental ballistic missile?
In a word: probably. That's the working assumption.
During military parades in Pyongyang in 2012 and 2013, North Korea showed off a three-stage missile, or rather a replica or one, on the back of a mobile launcher. It was the KN-08, called the Hwasong-13 in North Korea, a missile with a theoretical range of 11,500km. San Francisco is 8,850km from North Korea.
The first stage appeared to use four Scud engines with four small steering engines used to control the missile's flight, and steering engines in the second and third stages, according to Arms Control Today.
Then, during a similar parade in 2015, North Korea displayed a mock-up of a KN-14, an ICBM that is shorter than the KN-08 and appears to have only two stages. It is thought to have a range of up to 9,977km.
"In theory, these can reach the west coast of the United States," said Michael Elleman, senior fellow for missile defence at the International Institute for Strategic Studies.
A report by rocket experts John Schilling, Jeffrey Lewis and David Schmerler for the 38 North specialist website estimated that the KN-08 would work only 30-40 per cent of the time during its early operation, while the KN-14 looked to be 50-60 per cent reliable.
North Korea also has a space launch vehicle, the Unha-3, which it used to put a satellite into orbit - albeit a wobbly orbit - in February last year.
This could be pressed into service as a crude ICBM, Schilling wrote in a commentary for 38 North. "An ICBM variant of the Unha could be sufficiently similar to the space launch vehicle in that it would be very likely to succeed, making it a good candidate for a political demonstration even though the Unha would make for a poor missile," he wrote.
So, although North Korea has shown the world only the mock-ups, analysts and governments are operating on the assumption that North Korea is working on building these missiles.
"In North Korea, clearly we see now a combination of both intercontinental ballistic missile capability, as well as an effort to put a nuclear warhead on that intercontinental ballistic missile," General Joseph Dunford, chairman of the Joint Chiefs of Staff, said at the Brookings Institution in February. "So North Korea not only threatens South Korea, not only threatens the region, but now presents a threat to the homeland as well," he said.
Do these missiles actually work?
Well, we don't know because North Korea has never tried to fire them. But its recent engine tests and medium-range missile launches suggest it's working hard on them.
"For me, their biggest challenge is getting a large, two-or three-stage missile to actually work and for them to have confidence that it will work," said Elleman of the IISS.
After a string of embarrassing failures while launching the Musudan intermediate-range ballistic missile last year - only one of seven tests succeeded - Elleman thinks that North Korea will need to work on its Musudan engine and have a higher level of confidence that it can work before adding it into one of the stages of an ICBM.
Anyway, North Korea learns from failures as well as from successful launches.
"Even a failure might put the North on a path to success," Schilling wrote. "This is literally rocket science, one of the archetypal hard problems, and success can only be achieved through perseverance." The first American ICBM, the SM-65 "Atlas," failed 26 seconds into its maiden flight, he noted.
It's one thing to make a missile fly, but it's another thing to make it land where you want it. And North Korea has not shown any evidence that it has made a re-entry vehicle capable of surviving the extreme changes in temperature and the vibrations associated with bringing a missile back into the atmosphere.
Can they attach a nuclear warhead to these missiles?
With its last nuclear test, in September 2016, North Korea said that it could now make warheads small enough to fit onto a missile. The North Korean state propaganda machine had previously published a photo of Kim Jong Un with what it said was a miniaturised nuclear weapon.
Again, this is unproven. But there's a widespread recognition that North Korea, given its stated ambition and tangible efforts, will be able to achieve this sooner or later, if it hasn't already.
The month after North Korea's last nuclear test, James Clapper, the last director of national intelligence in the Obama administration, said that he assumed North Korea can do it.
"We ascribe to them the capability to launch a missile that would have a weapon on it to reach parts of the United States, certainly including Alaska and Hawaii," he said at the Council on Foreign Relations.
So the working assumption is that North Korea has an intercontinental ballistic missile and a warhead small enough to attach to it. Again, the question is whether it can successfully fire it, and whether it can successfully bring it back down to earth in one piece - and on a target.
Should people in Seattle and San Francisco be freaking out?
No, but they should be worried.
"Yes, as a looming threat, not a current threat," said Philip Coyle, a California-based senior science fellow at the Centre for Arms Control and Non-Proliferation and a former assistant secretary of defence. "North Korea does not yet have a long-range missile that can reach California. North Korean missiles can't even reach Hawaii, but time is not on our side."
For years, officials had been saying that North Korea wouldn't be able to master any of this technology. But analysts like Jeffrey Lewis at the James Martin Centre for Non-Proliferation in Monterey, California, say that it is just a matter of time until North Korea succeeds in its goal.
"It doesn't matter if it's today or tomorrow or next week or next year - that's where this is heading," Lewis told the Washington Post after a salvo of missiles from North Korea last month. "But we have no plan other than saying this is unacceptable or that it won't happen," he added, referring to President Trump's January tweet.
What can the US do to stop North Korea?
On a trip to Asia in March, Secretary of State Rex Tillerson said that the Obama Administration's policy of "strategic patience" - waiting for sanctions to hurt so much that North Korea returns to denuclearisation talks - was over. There has been increasing talk about military strikes, and Tillerson said in Seoul that "all options are on the table". While the United States has the technical capability to take out North Korean missiles, there are two big problems.
One: North Korea is no longer launching missiles from a fixed gantry - a process that can easily be spotted by satellites - but is using road-mobile launchers, which can be rolled out from a tunnel or hangar in a very short period of time.
Plus, North Korea has been working on solid fuel technology, so the missile is loaded and ready to launch from the moment it is rolled out, unlike with the older liquid-propelled rockets that required fuelling once the missile was in place.
Two: There's the not insignificant matter of the 25 million people who live in greater Seoul and would be at risk if North Korea retaliated for a pre-emptive strike by unleashing the conventional artillery lined up on the Demilitarized Zone, just 50km from the South Korean capital. The risk of strikes on Seoul has long constrained any talk of pre-emptive military action against North Korea, and that risk remains today.
We're now waiting to see what approach the Trump Administration takes towards North Korea.
For his part, former Obama Administration official Coyle said that direct talks between Washington and Pyongyang were the only answer.
"More than 15 years have passed since the United States last held serious negotiations with North Korea. North Korea used that time to test and build more and more missiles, to develop nuclear weapons, and conduct five nuclear tests," Coyle said.
"The US should not waste any more time and proceed to direct talks with North Korea without preconditions. If China can be engaged in parallel all the better, but only through direct talks will North Korea take the US seriously," he said.
Could the United States shoot down an ICBM?
Maybe, but it's tricky.
The US, Japanese and South Korean navies all operate Aegis warships designed to intercept shorter and medium range missiles. They could technically intercept an ICBM but only if the warship was very close to the missile's trajectory during the first or last few minutes of its flight, Schilling wrote for 38 North.
The US National Missile Defence system, based at fixed sites in Alaska and California, could probably intercept an ICBM but this would be of no use in protecting American allies, Schilling wrote. In a piece in January, Elleman laid out four reasons why it would be difficult for the US to intercept an ICBM.
