Analysis by Stephen Collinson, CNN

(CNN) -- Washington elites have long regarded war with North Korea as all but unthinkable. Yet, obscured by the wild twists and daily cacophony of the Trump presidency, the conventional wisdom is changing.

While President Donald Trump rattles sabers on Twitter and slams "Rocket Man" Kim Jong Un, there is also a perceptible hardening of tone among senior officials. Military action to halt North Korea's march to a missile tipped with a nuclear warhead that could hit the US mainland appears to be a growing possibility.

Trump upped the rhetoric another notch in an interview with Fox Business Network broadcast Sunday, in which he said Washington was "so prepared, like you wouldn't believe" for any contingency with Pyongyang.

"You would be shocked to see how totally prepared we are if we need to be," Trump said. "Would it be nice not to do that? The answer is yes. Will that happen? Who knows, who knows."

Trump's power to shock has been eroded by the extraordinary spectacle of his nine months as President.

Yet it's still stunning to hear an American President speaking so openly about the possibility of a war, that could, under some scenarios, cause the most devastation of any US conflict, at least since the Vietnam War.

There are no immediate signs that the administration is preparing for military action, for instance through evacuations of US military families in South Korea, or with a buildup of troops or materiel.

Yet it is also possible that the hardening of the administration's rhetoric and the narrowing window for diplomacy to work represent a significant moment in the evolution of a crisis that could ultimately define the Trump presidency.

The potential humanitarian, military and diplomatic cost of a war with the reclusive dynastic state has long been cited as the reason why it should and would never happen. Warnings about the North's thousands of rockets and artillery shells that could rain down on Seoul and threaten millions of people, reflect the reality that thriving, democratic South Korea is a nation hostage to its geography, unpredictable Northern brethren, and any decision by its ally the United States to launch a preemptive strike.

Other considerations, including the prospect of a collapse of the North Korean state and a mass refugee crisis, not to mention a dangerous escalation of US-China tensions, have also meant that the prospect of a war with Pyongyang has remained largely a theoretical proposition for half a century.

But Trump sent regional anxiety soaring when he warned the US might rain "fire and fury" on North Korea in August and later said America's military forces were "locked and loaded."

On one hand, Washington's toughened rhetoric can be put down to the raising stakes of the showdown. North Korea's ballistic missile launches and nuclear test this year mean that Trump will be the President who faces the dilemma that his predecessors have long dreaded -- what to do about an unpredictable dictator, with the power to hit the US mainland with a nuclear-tipped, long-range ballistic missile.

'Well, let's hope diplomacy works'

There is growing concern, quietly expressed in private conversations in Washington among foreign policy experts, members of Congress, and former national security officials, that war is becoming increasingly possible.

Many well-placed people are beginning to wonder whether there is a way out.

Senior officials, speaking over the last few weeks, have spoken more forthrightly and publicly about the possibility of conflict in ways that are raising questions about the administration's approach.

Last Sunday on CNN's "State of the Union," Secretary of State Rex Tillerson promised to keep up diplomacy until "the first bomb drops."

His comments could be interpreted as a willingness to never give up diplomacy, even though Trump told him in a recent tweet that he was "wasting his time."

Or Tillerson could be seeking to widen his leverage with a credible threat of force: The perception that the US could never use force on the Korean Peninsula clearly erodes the strength of its diplomatic position.

But his comments could also carry a darker interpretation.

Last week, CIA Director Mike Pompeo warned that the US should behave as though North Korea is close to the "final step" of bringing 320 million Americans within reach of a nuclear bomb. In a briefing in October, White House Chief of Staff John Kelly also spoke ominously.

"Right now, we think the threat is manageable, but over time, if it grows beyond where it is today -- well, let's hope diplomacy works," he said.

Former CIA Director John Brennan last week put the risk of US war with North Korea at least at one-in-five.

What about China?

Despite the rising risks, there are few signs of an intense administration diplomatic effort to alleviate the crisis beyond new sanctions passed over the summer against Pyongyang and backed by Russia and China.

The pace will increase next month when Trump visits Asia on a trip that will highlight the deepening North Korea crisis and could lead to more provocations by Pyongyang, including possible new missile tests.

That journey might provide a clue about the administration's strategy, since talking up the possibility of war would be a logical way to try to hike pressure on China to do more to convince its recalcitrant ally to change its behavior.

In line with the latest sanctions, China has tightened financial screws on North Korea, but it is unclear how far it is willing to go in isolating Pyongyang. Beijing has shown no sign that it has changed its long-held refusal to destabilize the Kim regime or eventually countenance a united Korea that it fears would be a US-allied state on its borders.

Many observers believe Washington overestimates China's influence on Kim, who has no relationship with Chinese President Xi Jinping.

If that view is correct, war talk could lock the United States into a cycle of escalation that takes on its own momentum without changing China's calculation.

Washington's position — that Trump will never accept North Korea having a nuclear weapon that could reach the United States -- is entrenched.

Similarly, most experts believe that Kim will never agree to give up a nuclear program that he sees as a guarantee of regime survival against a hostile United States that he has demonized to solidify his tyrannical rule.

There seems little room for compromise, or diplomatic creativity, and the prospect that sanctions could topple Kim's regime before he can deploy a long-range missile with a nuclear warhead appears dim.

Neither Trump, nor Kim is leaving himself any face-saving off ramps from confrontation.

That's why the war talk in Washington should be taken seriously.