Analysis by Chris Cillizza, CNN Editor-at-large

(CNN) -- First, an admission: I have no idea why President Donald Trump tweeted the following at 11:24 p.m. Eastern Time on Sunday night:

"To Iranian President Rouhani: NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE. WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!"

The likely reasons, as I see them:

Mired in a downward spiral in regard to the investigation into Russian interference in the 2016 election, Trump was trying to DRAMATICALLY CHANGE THE SUBJECT.

He saw Iranian President Hassan Rouhani's comments that a war with Iran would be the "mother of all wars" and DECIDED TO SEND A MESSAGE LOUD AND CLEAR.

Many people believe the former option to be the more likely. Maybe. Knowing Trump's thin skinned-ness, however, I wouldn't rule out the possibility that someone showed him Rouhani's quote -- or, even more likely, he saw it on cable TV -- and he lashed out.

Regardless of why Trump did it, here's what he did: Taunted an aspiring nuclear power with some of the harshest words we've heard from an American president.

Trump's thinking in regard to Iran is almost entirely informed by how he handled "negotiations" with North Korea. Trump called North Korean dictator Kim Jong Un "Little Rocket Man" and made clear that America's "nuclear button" was far larger than North Korea's. Fears ran rampant that Trump was tweeting the US into a war on the Korean peninsula. Then, somehow, Kim decided that a summit with Trump would make sense -- and the two sat down in Singapore last month, a meeting that Trump claimed had gone terrifically.

If it worked on Kim, Trump seems to believe, it will work on Rouhani. And it might! (To be clear: The summit "worked" in the sense it happened; denuclearization by the North Koreans is far from a done deal.)

But Twitter diplomacy -- which is one of the many things that Trump has ushered in as President -- isn't a tried-and-true approach to geopolitics. Especially since it's not entirely clear whether Trump actually checked with anyone in his administration before issuing the threat again Iran.

"The President consults with his national security team on a daily basis," said White House press secretary Sarah Sanders when asked directly whether Trump had run his tweet by any of the relevant parties in his administration. You would think that if Trump had, in fact, checked with his national security team, Sanders would have been able to answer the question a little (or a lot) less vaguely.

For Trump allies, this is all fine. Trump was elected as someone who knew how to deal with bullies and who wasn't afraid to do things very differently than the way they had been done in the past. It worked with Kim, they will note. Who's to say it won't work with Rouhani too?

The problem is, of course, what if it doesn't work? What if Rouhani doesn't react like Kim? What is he takes this threat as literal -- and makes moves to counter it? Diplomacy isn't a one-way street. Nor, typically, does a one-size-fits-all approach usually work.

The question is whether Trump has any speed except PEDAL TO THE METAL AT ALL TIMES. He's shown that gun-it style isn't without its merits in regards North Korea. But can he shift gears if it doesn't work as well with Iran? Does he understand -- or care about -- the complexities inherent in this sort of diplomacy? Or has he rendered those complexities irrelevant?

All of it comes back to the question that sits at the heart of Trump's presidency: Is he the exception or is he the new rule? Has he fundamentally altered the way nations negotiate -- in addition to realigning the Republican Party and conducting an all-out assault on fact? Trump clearly believes he has -- or he simply doesn't know any other way to be.

Either way, the stakes couldn't be higher. And Trump is charging FULL SPEED AHEAD.