The president of the European Council of national leaders, António Costa, has warned Donald Trump’s administration against interfering in Europe’s affairs, as analysts said the US national security strategy represented a seismic shift in transatlantic relations.

Released on Friday, the document claims Europe faces “civilisational erasure” because of migration and warns that a censorious EU “undermines political liberty and sovereignty”. It says the US will “cultivate resistance” in the bloc to “correct its current trajectory”. Analysts said the document confirmed not just the Trump administration’s hostility to Europe but its ambition to weaken it.

Costa said the signal that Washington would back Europe’s nationalist parties was unacceptable. Speaking on Monday, he said there were longstanding differences with Trump on issues such as climate change, but that the new strategy went “beyond that … What we cannot accept is the threat to interfere in European politics,” he said.

“Allies do not threaten to interfere in the domestic political choices of their allies,” the former Portuguese prime minister said. “The US cannot replace Europe in what its vision is of free expression … Europe must be sovereign.”

The strategy document was welcomed at the weekend by the Kremlin, which said it “corresponds in many ways to our vision”, while EU-US relations were strained further by a $120m (£90m) fine imposed by the EU on Elon Musk’s social media platform X.

Musk said on Sunday the bloc should be “abolished and sovereignty returned to individual countries”. The US deputy secretary of state, Christopher Landau, said the “unelected, undemocratic, and unrepresentative” EU was undermining US security.

Analysts said the document codified a US strategy first outlined by JD Vance at this year’s Munich Security Conference in a speech that accused EU leaders of suppressing free speech, failing to halt illegal migration and running from voters’ true beliefs.

“It transposes that doctrine into an officially backed state line,” said Nicolai von Ondarza, head of European research at the German Institute for International and European Affairs. “It really represents a fundamental shift in transatlantic relations.”

Von Ondarza said that in particular, “open US backing for regime change” in Europe meant that it was “really no longer possible for EU and national European leaders to deny that US strategy towards its European allies has radically changed”.

Max Bergmann, director of the Europe, Russia, Eurasia programme at the Washington-based Center for Strategic and International Studies, said political meddling in Europe to back far-right nationalists was now “a core part of America’s national strategy”.

Bergmann added: “This isn’t just a speech from a novice vice-president weeks into a new term. It is US policy, and they will try to implement it.” Moreover, he said, it could work: “In a fragmented political landscape, a 1-2% shift can change elections.”

EU leaders “will have to confront the fact that the Trump administration is coming for them politically”, Bergmann said. “Do they just accept that Trump is funding their political downfall? Or does this begin to cause an incredible amount of friction?”

Mujtaba Rahman, of the Eurasia Group risk consultancy, agreed. “The US is now officially committed, alongside Moscow, to interfering in European electoral politics to promote nationalist and anti-EU parties of the far right,” he said.

He said that if the document was US policy, the first election Washington would try to influence would be Hungary’s parliamentary ballot in April next year, in which the nationalist, Moscow-friendly incumbent Viktor Orbán faces a stiff challenge.

Minna Ålander of the Centre for European Policy Analysis said the policy document was “actually useful. It codifies in policy, in black and white, what has been evident all year long: Trump and his people are openly hostile to Europe.”

Europe’s leaders “cannot ignore or explain the fact away any more”, Ålander said. “Any hope for things to go back to the old normal looks increasingly ludicrous. Europe needs to finally seize the initiative and stop wasting time trying to manage Trump.”

Nathalie Tocci, the director of Italy’s Istituto Affari Internazionale, said Europeans had “lulled themselves into the belief” that Trump was “unpredictable and inconsistent, but ultimately manageable. This is reassuring, but wrong.”

The Trump administration had “a clear and consistent vision for Europe: one that prioritises US-Russia ties and seeks to divide and conquer the continent, with much of the dirty work carried out by nationalist, far-right European forces,” she said.

Those forces “share the nationalist and socially conservative views championed by Maga and are also working to divide Europe and hollow out the European project,” Tocci said, arguing that flattering Trump “will not save the transatlantic relationship”.

Jana Puglierin, a senior policy fellow at the European Council on Foreign Relations, said that while Trump remained erratic and the document may not ultimately amount to much, the US clearly wanted to “redefine what Europe means, to Europeans”.

The aim was to somehow establish that it is “us who are the aberration, that we have somehow forgotten our true values and heritage, and that European greatness therefore needs to be restored – with the help of ‘patriotic’ parties”, Puglierin said.

She said Europeans needed “to see the relationship much more pragmatically. Realise that endless flattery of Trump, promising to spending 5% of GDP on defence, or offering him breakfast with a king … is just not going to cut it”.

Von Ondraza said appeasement “has not worked on trade, it hasn’t worked on security, and it won’t prevent the US supporting Europe’s far right,” he said. “The bloc needs to articulate a strong strategy of its own, backed by a significant majority of members.”