The US president, who will address the annual gathering of global elites on Wednesday, has put the transatlantic alliance to the test with his demand to take over Greenland.
California’s Governor Gavin Newsom urged Europeans on Tuesday to stop playing nice with US President Donald Trump over Greenland, "develop a backbone" and "punch him in the face."
In blunt remarks to reporters at the World Economic Forum in Switzerland, the prominent Democratic politician called Trump "weak" and said the European Union should "push back very aggressively" against the US leader.
"He's good at exploiting weaknesses, but he backs down when he's punched in the face," Newsom said.
"You can't play all sides. Enough of the niceties," he added. "Stop trying to appease him. Fight fire with fire."
He called Trump's bid to take over Greenland "madness" but said the US president would not try to seize it "militarily."
"This whole excursion in Greenland is absurd and people need to recognise what they're up against and stand tall and firm, develop a backbone and speak with one unified voice. Punch him in the face," Newsom said.
The US president, who will address the annual gathering of global elites on Wednesday, has put the transatlantic alliance to the test with his demand to take over Greenland, saying the territory of Denmark is crucial to US national security interests.
The EU is weighing countermeasures after Trump threatened levies on eight European countries who spoke out in support of Denmark, though Washington has said any retaliatory levies would be "unwise."
EU chief Ursula von der Leyen told the meeting of global political and business elites that the EU's response would be "unflinching, united and proportional."
Denmark said on Tuesday it is ready to discuss matters related to the security and economy of Greenland with the US, but sovereignty is off the table.
"We can negotiate anything," Prime Minister Mette Frederiksen told the Danish parliament on Tuesday.
"But we cannot negotiate our very fundamental values, sovereignty, the identity of our countries and our borders. Our democracy."