On Wednesday morning, as President Donald Trump prepared to address the World Economic Forum in Switzerland and demand that Denmark hand over Greenland to the United States, members of the Danish and U.S. foreign policy establishment gathered at a think tank in Copenhagen.

The meeting had been scheduled to discuss the transatlantic alliance before Trump ruptured it, and brought together experts advising various governments on foreign policy from their positions in think tanks. The Americans tried to lower tensions, according to Philip Bednarczyk, an American who attended the gathering and works at the German Marshall Fund’s office in Poland. He said they suggested that U.S.–European cooperation was still possible and that there was a path through the crisis, despite Trump’s threats to slap tariffs on European countries or even launch an attack to get his way on Greenland.

Some of the Danes responded by floating the idea of a version of NATO without the U.S., he said.

Though Trump backed down by the end of the day, his two weeks’ worth of assaults over Greenland have rattled European diplomatic officials like nothing in recent memory, according to several who spoke to HuffPost. (All requested anonymity because they were not authorized to speak to the press.) They said Trump sowed chaos within their governments, leading to what appears to be a permanent shift in thinking toward skepticism of the U.S.