Lyse Doucet: Trump is shaking the world order more than any president since WW2

On day one, he put the world on notice.

"Nothing will stand in our way," President Donald Trump declared, to thunderous applause, as he ended his inauguration speech in a cold Washington winter on this day last year, at the start of his second term.

Did the world fail to take enough notice?

Tucked into his speech was a mention of the 19th Century doctrine of "manifest destiny" – the idea that the US was divinely ordained to expand its territory across the continent, spreading American ideals.

At that moment, the Panama Canal was in his sights. "We're taking it back," Trump announced.

Now that same declaration, expressed with absolute resolve, is directed at Greenland.

"We have to have it," is the new mantra. It's a rude awakening in a moment fraught with grave risk.

US history is littered with consequential and controversial American invasions, occupations, and covert operations to topple rulers and regimes. But, in the past century, no American president has threatened to seize the land of a longtime ally and rule it against their people's will.

No US leader has so brutally broken political norms and threatened long-standing alliances which have underpinned the world order since the end of World War Two.

There's little doubt that old rules are being broken, with impunity.

Trump is now being described as possibly the US's most "transformative" president - cheered by supporters at home and abroad, alarm among others in capitals the world over, and a watchful silence in Moscow and Beijing.

"It's a shift toward a world without rules, where international law is trampled underfoot, and where the only law which seems to matter is the strongest with imperial ambitions resurfacing," was French President Emmanuel Macron's stark warning on the stage at the Davos Economic Forum, without directly mentioning Trump by name.

There is mounting concern over a possible painful trade war, even worry in some circles that the 76-year-old Nato military alliance could now be at risk if, in the worst case scenario, the US commander-in-chief tries to take Greenland by force.

Trump's defenders are doubling down in support of his "America First" agenda, against the post-war multilateral order.

When asked on BBC Newshour whether seizing Greenland would violate the UN charter, Republican congressman Randy Fine said: "I think the United Nations has abjectly failed in being an entity that supports peace in the world and, frankly, whatever they think, probably doing the opposite's the right thing."

Fine introduced a bill called "Greenland Annexation and Statehood Act" in Congress last week.

How do America's anxious allies respond, when it seems nothing will stand in Trump's way?

Many phrases have peppered this past year of diplomatic contortions over how best to deal with the US's unpredictable president and commander-in-chief.

"We need to take him seriously but not literally," comes from those who insist this can all be sorted out through dialogue.

It's worked, but only to a point, on trying to forge a united response with Europe to Russia's blistering war in Ukraine.

Trump often veers, from one week to the next, from espousing positions close to Russia's, then tilting towards Ukraine, then bolting back into Russia's orbit again.

"He's a real estate mogul," says those who see in Trump's maximalist positions his deal-making tactics from his New York property days.

There's an echo of that in his repeated threats of military action against Iran – although it's clear military options are still on his now crowded table.

He doesn't talk like a traditional politician," explains his top diplomat, the US Secretary of State Marco Rubio when he is repeatedly questioned about Trump's tactics. "He says and then he does," is his highest praise for his president against what he derides as the dismal record of previous incumbents.

Rubio has been one of the principal voices trying to backpedal Trump's threats on Greenland, underlining that he wants to buy this vast strategic ice sheet, not invade it.

He pointed out that Trump has been exploring options to purchase the world's largest island, to counter threats from China and Russia, since his first term in office.

But there is no denying Trump's bully tactics, his contempt for collective action, his belief that might is right.

"He is a man of transactions and brute power, mafia style power," says Zanny Minton Beddoes, editor-in-chief of the Economist magazine.

"He doesn't see the benefit of alliances, he doesn't see the idea of America as an idea, a set of values; he doesn't give two hoots about that."

And he doesn't hide it.

"Nato is not feared by Russia or China at all. Not even a little bit," Trump told the New York Times in a wide-ranging interview earlier this month. "We're tremendously feared."

If security was the issue, the US already has forces on the ground in Greenland and under a 1951 agreement could send in more troops and open more bases.

"I need to own it," is how Trump flatly puts it.

And he often makes it clear, "I like to win." There's a growing body of proof that's what it is about.

His policy back flips in the past year have been baffling.

In the Saudi capital Riyadh in May, we watched how his major speech on his first foreign trip of his second term met a rapturous reception.

Trump took aim at the American "interventionists" whom he excoriated for having "wrecked far more nations than they built... in complex societies that they did not even understand themselves."

In June when Israel attacked Iran, Trump reportedly warned Israel's Prime Minister Benjamin Netanyahu not to put his diplomacy at risk with his military threats against Tehran.

By the end of the week, when he saw Israel's success in assassinating top nuclear scientists and security chiefs, Trump exclaimed: "I think it's been excellent."

"Sane-washing" was the phrase coined months ago by Edward Luce of the Financial Times to describe the world's polite portrayals of Trump, the succession of leaders landing at his door with glittering gifts and gilded praise to try to win him over to their side.

"Trump's apologists – a more numerous crowd than true believers - work round the clock to sane-wash his policies into something coherent," Luce wrote in his latest column.