On Friday, Donald Trump tried to walk back his claim that President Obama "is the founder of ISIS" in the most Trump way possible.

He simply blamed the media for taking him so "seriously." "THEY DON’T GET SARCASM?" he tweeted of CNN’s coverage:

Ratings challenged @CNN reports so seriously that I call President Obama (and Clinton) "the founder" of ISIS, & MVP. THEY DON'T GET SARCASM? — Donald J. Trump (@realDonaldTrump) August 12, 2016

I love watching these poor, pathetic people (pundits) on television working so hard and so seriously to try and figure me out. They can't! — Donald J. Trump (@realDonaldTrump) August 12, 2016

What makes Trump’s new excuse so absurd — and so unnerving — is what it says about how he’d fare as president. People all around the world tend to take what the president of the United States says very seriously. Which is why presidents don’t usually make a habit of communicating through sarcasm or by saying things and then claiming they weren’t serious.

Presidents don’t go out and constantly "joke" about invading countries, or about their economic policies, or about their political opponents being terrorists. They tend to put thought into what they say, because the risk of being misunderstood is too high. The fact that CNN (and others) will take what you say seriously is the whole point.

The media had every reason to take Trump’s ISIS comments seriously

This whole flap started on Wednesday when Trump called Obama the "founder of ISIS." ("Hillary Clinton is the co-founder," he said.)

Conservative pundit Hugh Hewitt asked Trump if that’s what he really meant in an interview on Thursday. Trump stood his ground: Like many conservatives, he believes Obama and Clinton’s policies in Iraq allowed ISIS to expand, and to him that’s the same thing as Obama and Clinton "founding" ISIS.

HUGH HEWITT: I think I would say they created, they lost the peace. They created the Libyan vacuum, they created the vacuum into which ISIS came, but they didn’t create ISIS. That’s what I would say. DONALD TRUMP: Well, I disagree ... I mean, with his bad policies, that’s why ISIS came about. ... If he would have done things properly, you wouldn’t have had ISIS. ... Therefore, he was the founder of ISIS. HUGH HEWITT: I’d just use different language to communicate it.

It’s pretty clear that Trump wasn’t joking. In fact, he seemed keen to insist that "founder" was the correct word here.

Set aside the fact that Trump is wrong on the merits here — the rise of ISIS involved a multitude of factors that Obama and Clinton were largely not a part of. Set aside the fact that Trump is stretching the definition of "founder" here. The key point is that this was not sarcasm. Trump was trying to make a point here, and now he’s upset that the media has taken that point "so seriously."

What it means for a president to be "joking"

Any successful presidential candidate usually needs two key traits, argues David Greenberg, a historian at Rutgers University: spontaneity and discipline. But each needs to be deployed at the right time.

Trump has the spontaneity: His shoot-from-the-hip bluntness is one reason he’s so popular with voters. "There is this kind of long tradition in our politics, especially in the last 30 or 40 years, of valuing candidates who are spontaneous and unfiltered," says Greenberg. "Because there is so much spin and crafted talk in politics that we get frustrated with it, we naturally respond to people that seem more candid."

But any good presidential candidate also needs discipline — in part because the presidency requires it, particularly around delicate subjects like diplomacy or managing the financial system, where one stray remark can cause a crisis. And Trump utterly lacks discipline. He puts himself in the headlines with inflammatory remarks almost daily — and can’t seem to help himself.

"He enjoys making provocative statements, and because he is not a seasoned politician he doesn’t know when it will misfire," says Greenberg.

Trump takes this lack of discipline one step further with another key habit: He never apologizes. His campaign usually just tries to flatly deny that he said anything or stretch the meanings of words so far they lose all semblance of what was obviously said, or else Trump just claims he was joking.

"That’s a very dangerous quality for someone who wants to become president," my colleague Zack Beauchamp writes. "A poorly phrased statement by the most powerful person in the world doesn’t just help amplify bad ideas — it can actively cause an international crisis."

Donald Trump hates lies, but can't tell the truth