President Trump assured us earlier this week that he would play hardball with Kim Jong Un in their upcoming meeting. “It would be very easy for me to make a simple deal and claim victory,” Trump said. “I don't want to do that. I want them to get rid of their nukes.”

His tweets on Friday tell a different tale.

With news breaking that the North and South Korean leaders agreed to work toward the “common goal” of denuclearization and a formal end of the 65-year-old war on the Korean Peninsula this year, Trump was more ebullient than most.

“KOREAN WAR TO END!” he exclaimed in ALL CAPS.

He later commended Chinese President Xi Jinping and talked about the peace “process” as if had just concluded. “Without him it would have been a much longer, tougher, process!” Trump exclaimed again.

This is premature, to say the least. If there's one thing everyone agrees upon, it's that the “process” is really just beginning. The news was big, if not unprecedented, but we've had agreements between North and South Korea before, and they haven't panned out.

Trump's tweets weren't just spiking the football but “spiking the ball while still in the locker room before the coin is tossed to start the game,” said Thomas Weiss, a scholar at the City University of New York who has studied North Korea.

As The Post's Anna Fifield notes, talks between Korean leaders in 2000 led to the South Korean president getting a Nobel Peace Prize. But it was later revealed that the meeting included a $500 million payoff to the North, and six years later North Korea detonated its first nuclear weapon. President Bill Clinton in 1994 prematurely declared a deal that a denuclearization deal meant “an end to the threat of nuclear proliferation on the Korean Peninsula.” And President Jimmy Carter in the late 1970s floated a U.S. troop withdrawal from the peninsula before negotiations fell apart.

Even the photo-op hug between Kim and South Korean President Moon Jae-in is hardly unprecedented. In fact, it looked a lot like the one between Kim's father, Kim Jong Il, with then-South Korean President Kim Dae-Jung in 2000.

None of which is to say today isn't significant or that Trump's posture toward North Korea — and the work toward tough sanctions at the United Nations — hasn't borne fruit. We could be on the precipice of a breakthrough, and even Trump's critics credit him for helping get to that point.

But the combination of Trump's lack of diplomatic acumen and his apparent desire for a big, presidency-changing win have to be taken into consideration here. Trump has great latitude to handle this situation himself, and he has assured us he'll be tough and demanding — that he might even just walk away.

And yet, at almost the same time, he has talked about the process as if he has already had a huge, measurable impact, and he appears enamored with the positive press he has received.

In a Thursday appearance on Fox News, Trump was giddy about showing pictures of Kim meeting with now-Secretary of State Mike Pompeo. “We have incredible pictures of the two talking and meeting which I'd love to release.” Later in the interview, he suggested North Korea had already made substantial concessions. “They've given up denuclearization, testing, research,” Trump said. “We're going to close different sites. And I'm saying to myself, wait a minute. All of these things he's given up, and we haven't even really that much asked them because we would have asked them but they gave it before I even asked.”

(There are also indications that North Korea's increasing willingness to talk could have to do with a damaged nuclear test site.)

Trump added in a public appearance Friday: “When I began, people were saying [peace] was an impossibility … And now we have a much better alternative than anybody ever thought possible.”

This could simply be the kind of good cop-bad cop approach that Trump seems to enjoy. But he's not exactly playing down the prospects of what could come from his meeting with Kim. He's increasingly invested in its success, and he seems to regard the progress made so far as being more ironclad than almost everyone else does.

He may have just been speaking loosely when he said North Korea has already “given up denuclearization” — it has merely said it would pause its program while talks are underway — but to the extent he's anxious to take its assurances, end the Korean War and maybe bring U.S. troops home, it's not unreasonable to think he might be tempted to “make a simple deal and claim victory.”