At the start of March, Norwegian marine fuel supplier Haltbakk Bunkers refused to service a United States warship, calling on others to boycott the US fleet.

Haltbakk CEO Gunnar Gran appeared to have been incensed at Ukrainian President Volodymyr Zelenskyy’s public humiliation in the White House by US President Donald Trump for allegedly being ungrateful for US military support to defend his country from a Russian invasion.

“Huge credit to the president of Ukraine restraining himself and for keeping calm even though USA put on a backstabbing TV show. It made us sick. … No Fuel to Americans!” the company wrote in a Facebook post.

The company later deleted the post, and the Norwegian government quickly insisted that US warships would continue to enjoy “the supply and support they require”.

But the incident highlighted the dependence of US forces in Europe on local suppliers and government goodwill.

There have been moments in history when European refusal to assist US forces has greatly complicated US operations.

At the outbreak of the 1973 Arab-Israeli War, both Greece and Cyprus refused to allow US ships and planes helping Israel to refuel, forcing them to rely on British assistance.

Days before then-President George W Bush’s invasion of Iraq in 2003, Turkiye refused to allow US planes to use its air force base at Incirlik or to cross Turkish airspace.

Partly for such reasons, US forces have built redundancies into their supply chain.

The US Sixth Fleet has a major resupply base in Greece’s Souda Bay near Chania, Crete, whose mayor in 2005 wrote to the US ambassador saying, “We don’t want your warships. We want your cruise ships full of doctors and lawyers.”

Demetries Andrew Grimes was US naval attache to Greece at the time and in reaction to that expanded US access from three to 11 ports because other mayors found the offer attractive.

“A single small ship that comes in to use a port facility will run between $80,000 and $120,000 a day, [including] the water and the fuel and the supplies and the trash removal,  tugboat operations. … We were spending about 350 million euros [$379m] a year in Greece just on bunkering fuel,” he told Al Jazeera.

In interviews with Al Jazeera, European NATO officers painted a picture of seamless cooperation.

“Military-to-military it’s business as usual,” a European military source told Al Jazeera. “We have no concerns whatsoever about the US commitment to its obligations in Europe. We just need to keep our head down, do a good job and be a good ally.”

Keir Giles, Russia and Eurasia expert at Chatham House think tank, told Al Jazeera that Haltbakk’s refusal of bunkering service was “counterproductive” because it alienated “precisely people that we need to keep on side, which is the US forces that are actually present in place”.

Changing assumptions?

Until now, the assumption was that the US saw European security as vital to its own.

“The access we have in Europe with our ports and bases from Spain to Italy to Greece to Türkiye to Germany – they’re there for our benefit,” retired US General Ben Hodges, who commanded US forces in Europe from 2014 to 2018, told Al Jazeera. “They’re not guarding Greeks or Turks or Germans.”

For instance, any Russian marine traffic sailing from St. Petersburg into the Atlantic Ocean has to cross Denmark’s Skagerrak Strait, less than 20km (12 miles) across at its widest point.

NATO officers told Al Jazeera that is an area where a sea denial operation can bar even Russian nuclear-armed submarines from getting through.

Russia has an alternative route into the Atlantic through the Barents Sea, but that is guarded by the navies of Norway and the United Kingdom, and the passages around Greenland, Iceland and Norway are sometimes referred to as a “kill zone” for Russian navy ships and submarines.

Yet the Trump administration has offended Denmark by asserting it will seize Greenland, a semiautonomous Danish territory, and it has offended Norway and other European allies by saying it will not defend Europeans who “don’t pay” their fair share to NATO, calling its mutual defence clause into question – something no other US president has done.

Most recently, Trump has threatened Canada.

“These actions, threatening Canada, threatening Denmark, will have consequences for us,” Hodges said. Asked if he thought there would be more incidents, he said, “It’s possible.”

Some experts told Al Jazeera the Trump White House has abandoned the decades-old doctrine of making common cause with Europe on security.

“The United States navy will have a strong interest in [these forward positions]. Will the Trump administration share that interest? That’s a whole other question,” Giles said.

“What’s happening in Europe now is what happened in Iraq and Libya years ago – America’s departure is leaving a security vacuum,” said retired Greek General Andreas Iliopoulos, a former deputy commander of the Hellenic army.

“If the US tries to do this reset with Russia in the way Trump is doing it, then these bases in Europe lose all their strategic value. That’s clear,” Iliopoulos told Al Jazeera. “The Russian threat has ceased to exist. Trump and Putin are acting like allies at the moment.”

The attraction for Trump in a security understanding with Russia is “to draw Russia away from China”, Iliopoulos said, but it is also likely about cost savings.

The US European Command (EUCOM) has about 84,000 personnel stationed in Europe, more than a third of its total overseas personnel. The US pays the full personnel and equipment costs but benefits through arms sales to Europe. Europe pays a third of basing costs but also enjoys income from basing.

Doubts about the US commitment to European security have undermined faith in NATO’s mutual defence guarantee. US Defense Secretary Pete Hegseth has reaffirmed it, but Trump has made it conditional on defence spending levels he has not defined.

Many Europeans have wondered whether US forces stationed in Europe would even be ordered into action in the event of an attack.

“Let’s not rule out some very big surprises if the anticonstitutional nature of the Trump-Musk actions continue to a point where there finally starts to be some signs of resistance from within the US system,” Giles said, referring to Trump assigning billionaire Elon Musk arbitrary powers to downsize the federal government.

Asked if the process of decoupling the US from Europe is irreversible, he said, “It will be soon, unless it is either resisted within the United States or something unexpected happens.”