North Korea’s burgeoning nuclear program is posing an increasingly serious problem for President Trump.

The rogue regime may have crossed a major threshold in its quest to become a fully-fledged nuclear power by producing a miniaturized nuclear warhead that can fit onto a missile, according to a U.S. intelligence assessment obtained by The Washington Post.

The development raises the stakes for Trump, who on Tuesday issued a stunning, provocative warning to North Korean leader Kim Jong Un.

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“He has been very threatening beyond a normal state, and as I said they will be met with fire, fury and frankly power, the likes of which this world has never seen before,” the president said, arms folded and voice raised, to reporters at his New Jersey golf club.

The intelligence assessment suggests North Korea is coming close to crossing the Trump administration’s red line of Pyongyang obtaining an atomic weapon that can strike America.

“If they had nuclear weapons that can threaten the United States, it's intolerable from the president's perspective,” national security adviser H.R. McMaster said in an interview that aired Saturday on MSNBC.

One of the biggest questions about Trump, who has never held office before, is how he would respond to a major international crisis.

Until now, his presidency has been marked by controversies, internal strife and political battles with Capitol Hill. But Trump has not yet been forced to deal with a terrorist attack, natural disaster or a new national security threat from a foreign government.

The North Korea situation is coming to a head during Trump’s summer vacation, a time when other presidents have seen their time away from Washington spoiled by controversy.

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Former President Obama’s approval ratings plummeted after his 2014 getaway in Martha’s Vineyard was marred by the Islamic State in Iraq and Syria’s (ISIS) beheading of U.S. journalist James Foley and violent protests after a fatal shooting by police in Ferguson, Mo.

Alarm in Washington over Kim’s pursuit of a nuclear weapon intensified in recent weeks as North Korea tested two intercontinental ballistic missiles (ICBM), including one that might have the ability to reach as far as Chicago.

In a victory for the Trump administration, the United Nations Security Council last weekend voted unanimously to sanction North Korea for the test. Trump phoned South Korea’s president Sunday night to discuss the vote and held a phone call the next day with White House chief of staff John Kelly and Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE to discuss the North Korean threat.

Pyongyang's ability to strike its adversaries with nuclear weapons remains shrouded in mystery. But it’s clear North Korea is accelerating its nuclear program; if it advances further, it could limit Trump’s options to respond, experts say.

“I think today’s the day, you need to mark it down in history, that North Korea [has] become a nuclear power,” said Harry Kazianis, director of defense studies at the Center for the National Interest. “This will be the biggest foreign policy test he will face.”

Though the North Koreans have yet to demonstrate they have all technologies necessary to strike the United States, such as working re-entry vehicle for its missiles, it’s only a matter of time before they do, Kazianis said.

“If they’ve already miniaturized a warhead, you have to assume they have the capability to hit the United States, otherwise we’re never going to do the things we need to do deter them,” he said.

Though North Korea is past the point of no return for having nuclear weapons, he said, the U.S. could prevent “next generation” capabilities, such as a three-stage rocket that could strike any North American target or a hydrogen bomb that is much more powerful than the atomic weapons Pyongyang possesses.

Kazianis suggested Trump give China 30 days to fully enforce international sanctions against North Korea, including the U.N. sanctions passed Saturday. Should China not take action, he said the U.S. should “completely reassess” its relationship with Beijing, including a long promised crackdown on Chinese trade practices and carrying out more aggressive confrontations against the country in the South China Sea.

Trump’s comments were meant to underscore he is serious about using military power — perhaps even America’s own nuclear arsenal — to stop North Korea’s nuclear program.

But others are warning Trump against taking drastic measures that could cause the volatile region to ignite.

Robert Gallucci, the chief U.S. negotiator during the 1994 North Korean nuclear crisis, cautioned that there remain many unknowns about the country’s nuclear program.

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For example, it’s unclear whether North Korea has successfully tested the miniaturized warhead and what yield the weapon has. Gallucci also highlighted the lack of a re-entry vehicle.

“You need to step back and look at situation from 30,000 feet. We’re still talking about how far away they are from having the capability to strike the United States with a nuclear-capable ICBM,” he said. What’s known about the intelligence assessment, he added, “does not mean they are there yet.”

But, Gallucci said, North Korea could be the “most critical” challenge Trump faces — even more than the conflicts in Syria or Ukraine.

“We could be hours away from an old-fashioned, big war on the Korean Peninsula,” he said. “This is not launching a few cruise missiles and you’re done. The North will respond.”

The North Korean problem has been on Trump’s radar since shortly after he was elected president. As he left office, former President Obama reportedly told Trump that the nation’s nuclear program would be the most urgent problem he would confront.

But experts say it’s essential that the administration get on the same page when it comes to a strategy, noting that mixed signals — where one day Tillerson indicates the U.S. is open to talks and another day Trump threatens Pyongyang — have been unhelpful.

“I would like everybody to think about whether we are so persuaded of the irrationality of the leadership of North Korea that we do not trust deterrence to work against these people, and we are so confident in our mistrust that we would risk another Korean war to try to deny them the capability to strike the United States,” Gallucci said.