If there is one word that defines Barack Obama's presidency, it would be "calm."

Obama's famous unflappability was occasionally put to bad use, as when he made excuses for CIA torture, allowed "the blob" to buffalo him into intervening in Libya, or failed to prosecute systematic mortgage fraud. But more often than not, his composure had a lot to recommend about it. Other things being equal, it makes good sense for a president to be cool and careful, especially when it comes to the use of force. The American military is the most powerful weapon that has ever existed, and it is a lot easier to break things than fix them.

Witness President Trump.

In Trump, we see the far worse downside of someone with the opposite temperament. Instead of an icy, collected president, we've got a distracted, angry idiot. And the diplomatic crises are rolling in.

Trump has already sparked a few minor tiffs by, among other things, yelling at the Australian prime minister for no reason, casually suggesting we should invade Mexico, and putting Iran "ON NOTICE."

But now we've got our first full-blown crisis. For basically no reason, Trump got into a standoff with North Korea — and the Japanese and South Koreans are understandably furious.

It's hard to know what got this idea into his head; possibly TV coverage of the apparent assassination of Kim Jong Un's half-brother, or ongoing North Korean missile tests (the most recent of which failed).

But whatever it was, by early April, Trump was saying that America would be willing to go it alone to restrain the North Korean nuclear program, and top military officials announced that the carrier strike group containing the USS Carl Vinson was steaming towards the region as a show of force. Probably as a chest-beating exercise, the military then dropped its largest non-nuclear bomb on ISIS fighters in Afghanistan.

Bizarrely, it later turned out the Carl Vinson was in fact thousands of miles away in the waters off southern Indonesia, en route to training exercises with the Australian navy. It remains unclear as to what the heck happened — whether it was deliberate deception, or there were some crossed wires in military communications, or the administration is still just horribly understaffed, or what.

But whatever happened, the South Koreans and Japanese were seriously upset. Koreans were downright enraged when Trump, relating a talk he had with Chinese President Xi Jinping to The Wall Street Journal, commented that he had learned that Korea had once been part of China. Not only is that not true, it faintly suggests a lack of commitment to Korean territorial integrity.

Worse, the whole ridiculous mess risks destabilizing a teetering yet dangerous enemy. North Korea is a poor, beleaguered country, founded by a brutal authoritarian and governed ever since through a cult of personality by that man's increasingly weird descendants. It has been an economic basketcase since the collapse of the Soviet Union, which subsidized it heavily. However, it has at least some marginal nuclear weapons, and perhaps more importantly, many thousands of very well-protected heavy artillery pieces perfectly positioned to strike Seoul, the capital of South Korea. That city's metro area has 25 million residents, lies only 35 miles from the border, and is also mostly ringed with mountains and rivers — making any evacuation difficult.

In other words, North Korea has a credible deterrent. It could not possibly resist the full weight of the American military for long, but it could inflict hundreds of thousands, or even millions, of casualties before it went down. (Not to mention that any all-out attack on the regime would then leave America with the responsibility of rebuilding a wrecked post-dictatorship society — something we have not managed very well of late.)

Like any sensible person who thought about the above facts for five minutes, Obama basically settled on a strategy of quietly preserving the status quo. North Korea remains under heavy sanctions that have been in place for decades now, but the regular bizarre provocations were met with calm condemnation, not hysterical threats and escalation.

For now it seems Trump has backed down from his tough-guy posturing. But not only did he display shocking disregard for the safety of millions of citizens of allied nations, he also badly harmed the diplomatic relationship with Japan and North Korea. The man is a menace.