For President Trump, his weekend excursion to Japan could have been a welcome respite from the political warfare back home, as he watched sumo wrestling and performed on the world stage.

Most presidents used such foreign forays to change the subject. Bill Clinton, in particular, would grow annoyed when reporters halfway around the world would press him about Whitewater or Monica Lewinsky or other domestic scandals.

But Donald Trump does things differently.

It was Trump, not the press, who embroiled himself in a major media controversy by appearing to side with Kim Jong Un against Joe Biden.

Among those crying foul are a number of conservative commentators, on Fox News and elsewhere, and such Republicans as Rep. Peter King of New York, who called the comments "wrong" and said, "politics stops at water's edge."

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The president has obviously settled on a strategy of attacking Biden early and often, while mainly ignoring the other 22 Democratic candidates. The former veep, meanwhile, is maintaining a light schedule, ignoring many of Trump's jabs and generally trying to act above the fray.

Even on his ceremonial visit to Japan, I think Trump could have gotten by with a couple of jabs at Biden. The "water's edge" adage has become an empty slogan. But what crossed the line — at least judging by criticism from his own side — was invoking a murderous dictator in denigrating a Democratic rival.

And if Barack Obama had quoted Kim to slap at a top Republican, the GOP would have gone haywire, and rightfully so.

Trump loves to shatter political norms, having long since learned that being over the top guarantees constant media coverage as the pundits debate whether this time he's gone too far.

But when North Korean media, in a slur attributed to the Dear Leader, said Biden is a "fool of low I.Q.," Trump couldn't resist. The president tweeted that he "smiled" when he heard that, adding: "Perhaps that's sending me a signal?"

TRUMP 'SMILED' WHEN NORTH KOREA CALLED BIDEN 'LOW IQ,' SUGGESTS CRITICAL EDITORIAL WAS A 'SIGNAL'

This might have been written off as a sleep-deprived tweet. But Trump didn't give an inch at a news conference, saying: "Kim Jong Un made a statement that Joe Biden is a low IQ individual. I think I agree with him on that."

I really don't care about the views of the Democratic front-runner from a man who kills his domestic rivals and who Trump himself once dubbed "Little Rocket Man" before praising him after two nuclear summits. Biden didn't immediately respond, but on Tuesday his camp called the remarks "beneath the dignity of the office." (Trump tweeted last night that he was "actually sticking up for" Biden because Kim called him a "low IQ idiot" and the president softened that to "low IQ individual. Who could possibly be upset with that?" Who, indeed?)

In the same initial tweet, Trump undercut his own national security adviser. John Bolton had said publicly, presumably with the boss's blessing, that North Korea's two recent ballistic missile tests were a clear violation of U.N. resolutions. There's no way the national security hawk was freelancing on that one.

The president said Pyongyang's firing of "small weapons" had "disturbed some of my people, and others, but not me," because he has confidence that "Chairman Kim will keep his promise to me."

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It was reminiscent of the time that Trump blindsided his first secretary of state, in the other direction, by tweeting that Rex Tillerson was "wasting his time trying to negotiate with Little Rocket Man."

In the end, Trump is the president; everyone else is staff. He'll ultimately be responsible if his nuclear gambit with North Korea falls short. But sometimes, as with Biden, he launches rockets that veer off course.