This is a glorious day for cynics, especially lazy ones. It doesn’t take much effort to find loopholes, inconsistencies and other deficiencies in the agreement signed by President Trump and Kim Jong Un.

Start with the fact that fulfilling the primary promise, denuclearization of the Korean Peninsula, would involve such a vast physical, logistical and scientific undertaking that it’s easy to bet it will never happen, at least not all of it.

There’s also the track record of deals North Korea broke before the ink was dry, and the lack of any evidence that this murderous Kim will prove more trustworthy than his murderous father or grandfather. Besides, why would China let him give up his greatest leverage when it could cost the Red puppet master a key buffer and major irritant against America?

Any or all of these could become deal killers. If so, that will become clear in time.

But today should be declared a holiday from nitpicking, a time to celebrate what has been accomplished instead of fixating on the possible pitfalls. It is an occasion to look forward with hope, instead of backward with suspicion.

Through that lens, the deal is a sensational triumph for much of the human race, one that could improve the security of hundreds of millions of people in America, both Koreas and Japan. It also lifts the spirits of anybody anywhere who believes in the possibility of peace on Earth.

Before our eyes, a promise is made to turn swords into ploughshares. As Joe Biden said on a far less significant occasion, this is truly “a big ­f–king deal.”

It is also a vindication of Trump’s approach to a problem that his three predecessors kicked down the road. Perhaps, if he had a choice, he also would have punted the problem to his successor.

But Trump didn’t have that option because over the last two decades, North Korea had been allowed to develop both nuclear weapons and long-range ballistic missiles. The end of the road was in sight and there was no room left to kick the can.

All that remained was for Kim to solve the final piece of the weapons puzzle: putting nukes on his missiles and successfully delivering them to the city of his choice, be it Tokyo, Los Angeles or New York — or all of the above.

That was a risk Trump and his military and security teams did not take. They were determined to solve the problem while there still was time.

Admittedly, there were moments — horrifying moments — when nuclear war seemed a likely outcome. In the beginning, the weapons were insults like “little rocket man” and “dotard.”

Less than six months ago, Kim escalated the tensions by saying, “The entire mainland of the US is within the range of our nuclear weapons and the nuclear button is always on the desk of my office.”

Trump, his counterpunching skills fully intact, hit back harder, tweeting that “I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!”

Experts scurried to calculate the human toll of a nuclear war, starting with the possibility that the 10 million people who live in and near South Korea’s capital of Seoul would be wiped out.

That would be just the beginning if Kim could deliver nukes to American cities.

The United States, of course, faced similarly awful scenarios during the Cold War, with the Soviet Union holding a huge arsenal and the ability to carry out massive strikes on American targets. But one essential difference was the assumption that Soviet leaders, whatever else they were, ultimately were rational people who knew they and their families would die, too, and so were unlikely to start a war they could not finish.

But this doctrine of “mutually assured destruction” is useless when the other side is not viewed as rational. Because North Korea became the Hermit Kingdom over the last 65 years and a virtual gulag for its citizens, strategists dared not assume Kim Jong Un was rational. Like the crazy man in the subway wielding a knife, he could not be counted on to make a logical assessment of the consequences if he struck first.

But Trump, in addition to the bellicose threats, also had another card up his sleeve. It was the China card, and he played it brilliantly.

His determination to make better trade deals for American workers led him to early and frequent engagements with President Xi Jinping. By all accounts, the two hit if off personally, but it probably mattered more that during Xi’s visit to Mar a Lago, Trump interrupted dessert to tell him that the US had just fired 59 cruise missiles at targets in Syria after Bashar al-Assad used chemical weapons.

Oh, what delicious chocolate cake, Mr. President!

Trump’s willingness to enforce the red line that Barack Obama created and then abandoned must have persuaded Xi, and therefore Kim, that they were dealing with a different kind of president. One who was willing to back his tough talk with tough action.

No doubt there are other calculations involving China and North Korea, including the impact of tightened United Nations sanctions on Kim’s teetering economy and the possibility the regime could collapse, sending a flood of starving Koreans into China.

There is also a strong possibility that Xi decided he could not fight Trump on both North Korea and trade, and is willing to give on the nuke issue in the hopes Trump will reward him on their tariff squabble, which is far more important for China’s domestic economy.

Whatever the full range of reasons, China began to behave differently, as when it publicly criticized Kim’s war threats and temporarily stopped buying North Korean coal last year. While China did not fully comply with UN sanctions, the message was powerful: Coal is the North’s most valuable export, and China its most important customer.

So something had to give, which is how the world came to be riveted on the tiny city state of Singapore.

A final thought on the larger lessons of American leadership. From the outset of his presidential campaign, Trump promised to pursue peace through strength and committed to an expensive rebuilding of our military.

He also offered a sharp break from the previous administration’s appeasement of Iran and its feckless “strategic patience” policy on North Korea, which was Obama-ese for doing nothing. Last summer, Susan Rice, Obama’s national security adviser, even urged Trump in an op-ed to “tolerate nuclear weapons in North Korea” rather than risk war.

Today, we celebrate the fact that he ignored her. And are reminded, happily, that elections have consequences.