And as details emerge about this latest ballistic-missile test, Melissa Hanham, an expert on the North Korean nuclear-weapons program at the Middlebury Institute of International Studies, has a response to Trump’s vow that what U.S. officials fear most from North Korea “won’t happen!” It has happened—or at least it may finally be time to start acting as if it has. She explains why below, in a conversation that I have condensed and edited for clarity.

Uri Friedman: I’ve seen your analysis that the missile North Korea just tested may have been longer-range than the last North Korean test of an ICBM, and potentially long enough to threaten U.S. cities like New York. Can you go into what’s behind that assessment and what the math is?

Melissa Hanham: Whenever a missile is launched, there are a few points of data that we immediately look for. One is where it was launched from, one is where it landed, the other is how high it went, and how long it took to fly. That data tends to trickle out pretty quickly from South Korean, Japanese, and American sources. Those numbers are still firming up right now.

When we analyzed the Hwasong-14 launch, [North Korea’s first test of an ICBM, on July 4], we were able to see that even though the missile only traveled just short of Japan, it went quite high up into the air, through the atmosphere, past the Space Station. That’s called a “lofted trajectory.” If you were to adjust that curve to the more energy-conserving range, toward the U.S., you would get a range that would put Alaska at risk.

However, we weren’t satisfied with just that number. When [the North Koreans] released photographs of the Hwasong-14, we did very careful measurements of each stage of the rocket, we made estimates of the fuel and oxidizer in each stage of the missile, the weight of each stage of the missile, and we did analysis of the video of the rocket launching to get a sense of the acceleration off the ground and therefore the thrust of the missile. And at that time we predicted that even though the test only showed [the missile] going about 7,000 kilometers, [the missile] was not tested to its full capability. In fact, we estimated that it would be more like a 10,000-kilometer range instead.

Friedman: What would a 10,000-kilometer range mean?

Hanham: Not just Alaska but all of the West Coast and most of the Midwest. So Chicago, Detroit.

Friedman: How does that compare to what we know so far about [today’s tested missile]?

Hanham: Today the data that’s coming in, which is still soft, is showing that along the ground, [the missile] went farther, it had a higher altitude, and it flew for a longer amount of time. So, no matter what, it demonstrated a farther range than the previous test. And if we make the assumption that this is the same missile [which has yet to be confirmed], then we would say that [the North Koreans] were probably trying to test the missile at a greater capacity, if not its greatest capacity.