The president of the United States just taunted the erratic leader of nuclear-armed North Korea the way that a 5-year-old would bully the unpopular kid in his class.

That isn’t a sentence I ever thought I’d write in my professional career. But I also never thought that Donald Trump, a real estate developer and reality TV star known for his public, years-long feud with actress Rosie O’Donnell, would be president of the United States. As president, Donald Trump has continued to exhibit some of the same patterns of behavior that served him so infamously well in the private sector and on the campaign trail. In Trump’s tweet taunting Kim Jong Un, he worked in a reference to his “much bigger and more powerful” ... nuclear button:

North Korean Leader Kim Jong Un just stated that the “Nuclear Button is on his desk at all times.” Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works! — Donald J. Trump (@realDonaldTrump) January 3, 2018

There’s something about this that’s funny. But it’s important to think seriously about the implications of Trump treating the nuclear standoff between the United States and North Korea as if it were a personal celebrity feud, or a joke.

This is an extremely tense military standoff where the two sides have no formal lines of communication and haven’t held any formal negotiations in years. A single misperception — a single moment of believing that the US might be about to attack — could cause North Korea to launch a preemptive strike. Millions of lives hang in the balance.

Some experts think this tweet, on its own, raises the temperature of the standoff and, as a result, the risk of conflict.

“Not only does Trump recklessly and buffoonishly try to out nuclear saber rattle Kim Jong Un, he denies the reality that North Korea is a nuclear armed state, thereby daring KJU to conduct additional tests to prove his capability,” Kingston Reif, the director for disarmament and threat reduction policy at the Arms Control Association, wrote after seeing the tweet.

“Spoken like a petulant 10-year-old. But one with nuclear weapons — for real — at his disposal,” Eliot Cohen, a professor at Johns Hopkins University, writes. “How responsible people around him, or supporting him, can dismiss this or laugh it off is beyond me.”

This is deadly serious

It’s important that we’re clear on the stakes of this conflict.

Should war break out, experts say that North Korea’s artillery could kill tens of thousands of civilians in Seoul, South Korea’s densely populated capital, within the first hours of a conflict. A protracted fight could lead to destruction on the Korean Peninsula on a scale unheard of since the Korean War in the 1950s, with hundreds of thousands of potential deaths on both sides.

The North’s nuclear missiles could easily reach Tokyo; most major American cities are also within their theoretical range. Imagine a worst-case scenario — a nuclear strike on New York City, hundreds of thousands of Americans dead in a catastrophe that would dwarf 9/11 by multiple orders of magnitude — and you start to understand what’s at risk here.

A disaster on this scale is hard for us to contemplate. But I’ve spent the past month talking to experts and policymakers about North Korea, and they have all said the same thing: War with North Korea is becoming more and more likely, owing both to North Korea’s developing nuclear program and the Trump administration’s aggressive response.

“We are far closer to actual conflict over North Korea than the American people realize,” Sen. Tammy Duckworth (D-IL), an Iraq War veteran and Purple Heart recipient, told me in an interview in December. “Everything we’re doing shows a military that, in my personal opinion, has turned the corner ... the president is likely to make this decision [to attack], and we need to be ready.”

The point is that this is real, and the threat of war should be handled carefully. But the man in charge — the US president — doesn’t seem to be taking it that seriously. He’s made casual threats about starting a war, seemingly without much forethought. His most famous North Korea comment, that the US would respond to North Korean provocations with “fire and fury like the world has never seen,” was improvised during an August meeting that was supposed to be about opioids.

Trump seems to think — at least in part — that the dispute is part of a personal contest between him and Kim Jong Un. It isn’t just the implied dick joke in the most recent tweet. It’s calling him “short and fat,” and saying that he’s a “sick puppy.” It’s the constant, unending references to the North Korean dictator as “Little Rocket Man.”

There is a serious risk of catastrophic war, and the president is fanning the flames

This reflects Trump’s longstanding approach to people he sees as enemies.

His feud with Rosie O’Donnell — in which Trump called her “fat” and “dumb,” among other things — goes all the way back to 2006, per a CNN timeline. Between June 2015 and today, the New York Times reports, Trump has insulted 410 people, places, and things on Twitter alone.

During the 2016 election, he implicitly bragged about the size of his penis at a Republican presidential debate, called his primary GOP rival Ted Cruz’s wife ugly, and threatened to jail Hillary Clinton if elected president. He said retiring Sen. Bob Corker (R-TN) “couldn't get elected dog catcher,” and that former FBI Director James Comey was a “disaster” who ran a “phony and dishonest Clinton investigation” and left the bureau’s reputation in “tatters.”

This combination of bluster and insult, in short, is the way that Trump approaches many things in his professional career. But in the case of North Korea, it has the potential to produce extremely dangerous results.

The issue isn’t really Trump’s Tuesday tweet. It’s that the repeated drumbeat of threats from Washington will convince North Korea that the United States is getting ready for war, making them potentially more likely to shoot first.

The ride isn’t funny anymore, if it ever was. I’d like to get off.