European officials knew the president’s win would threaten the fundamental precepts of the post-World War II order. But the speed at which it is unraveling has created a crisis of enormous proportions.

The front-runner to be Germany's next chancellor, Friedrich Merz, said that Europe cannot rely on US President Donald Trump honouring NATO mutual defence obligations and must become more capable of defending itself.

The US is likely to maintain its commitment to NATO, though it may reduce its troop presence in Europe as its priorities shift to the Indo-Pacific region, a top alliance official said.

New US Defense Secretary Pete Hegseth is expected to assume the role of backseat driver in his first in person meeting with European counterparts on Wednesday as the new Trump administration works to shift responsibility for Ukrainian and European security squarely to NATO and the EU.

European Union foreign policy chief Kaja Kallas said on Thursday that interactions between the United States and Russia showed Moscow had not given up its territorial goals in Ukraine, and that appeasing it would send a dangerous signal.