Gavin Newsom is warning US allies to confront "T-Rex" Donald Trump and stop "rolling over" to his demands, as European leaders grapple with a diplomatic crisis over the president's bid to take over Greenland.
The California governor, a contender to be the Democrats' presidential candidate for 2028, told leaders they were "paying the price" for not being tougher with Mr Trump when he returned to the White House a year ago.
His intervention at the World Economic Forum in Davos came as Mr Trump repeatedly threatened to impose additional 10 per cent tariffs on eight European countries who refuse to back his plan for American acquisition of the Danish territory.
Mr Newsom urged leaders, who are weighing up how to respond to a potential trade war, to "get serious" and "stand united".
"Well this is diplomacy with Donald Trump," he said.
"He's a T-Rex. You mate with him or he devours you, one or the other. The Europeans could be (devoured) if they continue down this path and process.
"They need to stand tall, stand firm, stand united. Look, a year ago we should have been having this conversation, and they didn't.
"And now you're paying the price - exactly what anyone, [any] objective observer would have anticipated we'd be where we are today."
The governor has been one of Mr Trump's most strident domestic critics at a time when leaders in Washington DC have appeared unwilling to confront the White House.
"I've seen this in the United States. The supine Congress playing both sides, you know, saying one thing on a text or tweet and another publicly."
"Just, I can't take this complicity. People rolling over," Mr Newsom added.
"I should have brought a bunch of knee pads for all the world leaders."
The US president has in recent weeks hardened his rhetoric on the future of Greenland.
In response, EU leaders have proposed beefing up Arctic security, suggested holding talks on the sidelines at Davos, and threatened to retaliate with a so-called "trade bazooka".
Many have been seeking to de-escalate the prospect of a tariff battle between the US and Europe, hoping instead to strike a compromise.
Ex-NATO boss warns 'time for flattering is over'
It comes as Mr Trump prepares to travel to the Swiss alpine town to address the summit in person on Wednesday, local time.
Former NATO chief Anders Fogh Rasmussen, who is also a former Danish Prime Minister, was among those at the gathering on Tuesday.
He had similar advice for world leader to that of Mr Newsom.
"It's really the future of NATO that is at stake," he told the Reuters news agency.
"The time for flattering is over. It doesn't work.
"The fact is Trump only respects force and strength. And unity. That's exactly what Europe should demonstrate right now."
EU 'should not hesitate' in Trump response, Macron says
Meanwhile, Mr Trump posted on social media a text message sent to him by Emmanuel Macron, in which the French president offered to bring together a meeting of G7 leaders after Davos, and questioned what his US counterpart was "doing on Greenland".
Mr Trump later posted an AI image of himself in Greenland, holding a US flag, and another image of him speaking to leaders next to a map showing Canada and Greenland as part of the United States.
Delivering a speech at the summit, Mr Macron said he did not plan to speak with Mr Trump.
Mr Macron warned in Davos that additional tariffs from the US could force the EU to use its anti-coercion mechanism "for the very first time" against their NATO ally.
“Can you imagine that?” he said, arguing that allied countries should be focusing on bringing peace to Ukraine. “This is crazy.”
In general, he said, the mechanism "is a powerful instrument and we should not hesitate to deploy it in today's tough environment."
He also used the speech to warn against Mr Trump's "new colonialism", describing it as a shift to a world "without rules".
"Where international law is trampled underfoot and where the only law that seems to matter is that of the strongest, and imperial ambitions are resurfacing."
ABC/wires
