For decades, presidential administrations have tried — and failed — to curb North Korea’s nuclear weapons program. The Trump administration’s approach so far has been both aggressive and confusing.

Three months ago, for example, Secretary of State Rex Tillerson released a statement that read: “The United States has spoken enough about North Korea. We have no further comment.” Does that mean negotiations are over? It’s not clear.

Tillerson insisted that America’s policy remains a denuclearized North Korea, not regime change, but it’s apparent that relations between North Korea and the United States are increasingly strained.

And tensions are likely to intensify after North Korea decided on Tuesday to conduct yet another missile test, this time firing an intercontinental ballistic missile, which traveled nearly 600 miles before it landed in the sea between Japan and North Korea.

Although the test doesn’t demonstrate North Korea’s capacity to fit such a missile with a miniaturized warhead, it’s a significant step in the regime’s efforts to develop the capacity to deploy long-range nuclear weapons.

To understand how close we are to full-scale conflict in North Korea, I recently reached out to Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies. Lewis focuses on nuclear nonproliferation, international security, and disarmament, and he is the author of Minimum Means of Reprisal: China's Search for Security in the Nuclear Age.

I asked Lewis to lay out some of the worst-case scenarios in North Korea.

Here’s what he told me.

Scenario 1: The North Koreans mistakenly believe that we are going to launch an attack on them, and Kim Jong Un does something crazy.

The big dilemma here is that, in North Korea at least, everything is organized around the fear that they will be invaded, and that Kim Jong Un will end up like Muammar Qaddafi in Libya or Saddam Hussein in Iraq. But unlike Qaddafi or Hussein, Kim has actually acquired nuclear weapons, and if you look at the missile testing they do, a lot of these are tests that have already been conducted. What they're doing, in fact, is practicing hitting airfields or other targets that the US would likely use to sustain an invasion. As far as we can tell, the North Korean theory is that on the first day of a potential war with America, if they just use a bunch of nuclear weapons — in South Korea, in Japan potentially — the damage will be so severe that we will be deterred from future aggression, or that the costs will be so high that a successful invasion will be impossible. But for this strategy to be effective, it means North Korea has to go nuclear first, to raise the stakes to an impossibly high level right at the beginning. My worry is that Trump says or does something incautious or imprudent, as he often does, which North Korea interprets as deadly serious and decides to escalate immediately to deter a potential invasion. It’s easy to see how things could get out of hand in a hurry.

Scenario 2: The North Koreans stage yet another provocation, only this time it goes too far and South Korea responds.

This scenario is a little bit Trump goes crazy and a little bit South Korea goes crazy, but I'll focus on South Korea. The North Koreans like to stage provocations. In 2010, for instance, they sank a South Korean ship and they shelled an island. Last year, they put a land mine on the DMZ [demilitarized zone] and blew the legs off a South Korean soldier. And the list goes on and on and on. So they're constantly testing the limits, constantly provoking. The scenario here is that North Korea goes one provocation too far and South Korea finally responds in kind. It's hard to imagine how this will play out. The South Koreans are increasingly committed to their ability to respond to these provocations, but they're terrified of a nuclear strike. They're developing ballistic and cruise missiles with the express purpose of killing Kim Jong Un. The idea is that they can eliminate [Kim] so that he won't be alive to give the orders to launch nuclear weapons. But if they try and fail to take out Kim, all bets are off. So my concern here is that North Korea is always staging provocations, but eventually they’ll go too far, and the situation will unravel.

Scenario 3: The Trump administration talks itself into a conflict it can’t contain.

This scenario is like Iraq in 2003, except it's a much bigger fiasco. So imagine Trump being humiliated by North Korea after he insists the situation is under control: He says North Korea is contained, and then they continually defy him with one provocation after another. Eventually, the administration convinces itself that regime change is the only viable option. So this is a case in which Tillerson's language of not talking to North Korea gets taken literally. Trump decides he's just going to isolate North Korea to the point where we do something similar to what we did in Iraq in 2003: gather forces in the region, round up a few allies, and get some kind of dim authorization from Congress for the use of force. And then, before you know it, we're involved in a major conflict. What I worry about here is that the Trump administration, like the Bush administration in 2003, talks itself into believing that this will be easy, and gets embroiled in a crisis it can't contain.

Scenario 4: North Korea’s pursuit of nuclear weapons finally spawns an arms race with Japan, which in turn extends to other regional powers.

Right now there's an aggressive cruise missile race in Asia. Not only do the Chinese have cruise missiles but so do the South Koreans and the Taiwanese. The North Koreans have mostly ballistic missiles. The only country so far that hasn't gotten involved in this arms race is Japan. But there are indications that Japanese Prime Minister [Shinzo] Abe wants to buy Tomahawk land-attack missiles from the United States, which would be an enormous enhancement in Japan's offensive capabilities and very alarming to North Korea and the Chinese. So the question here is: Will the North Korea's aggressive provocations finally push Japan to militarize? This would be a predictable response by Japan to North Korea's microaggressions. But it could dramatically destabilize the region by setting off a chain of destructive consequences.

Scenario 5: The North Korean regime collapses internally, creating a failed state.

If the government started to collapse, we'd likely see a return of the horrific things we saw in the ’90s, with famine and disease spreading over the country. But we'd also have armed factions fighting one another for power, and you can imagine a scenario in which the United States, South Korea, China, and others get sucked in. If North Korea does collapse, it won't be like East Germany; it'll be closer to Bosnia or Libya or Syria, and that means proxy conflicts and power vacuums. And remember: If the regime does fall, someone will have to go in there and secure those nuclear weapons, and there's no easy way to do that. This is probably the least likely scenario, but it is certainly possible. This is a very unstable regime, and we definitely can’t rule out a state collapse.

Watch: The North Korean nuclear threat, explained