In less than two months, U.S. President Donald Trump has upended decades of foreign policy. He has left NATO members questioning whether Washington will honor the trans-Atlantic alliance’s commitment to defend each other, if other European countries are attacked by Russia. He’s also made repeat overtures to Moscow and suspended most U.S. foreign aid.

That could impact foreign sales of the Lockheed Martin-produced F-35 and other advanced U.S. jets like the F-16. As Russia’s war in Ukraine grinds on, it’s become clear that Eastern European NATO members still have vast stores of Soviet-era weapons in their stockpiles that weren’t interoperable with Western weaponry.

A long-term plan to get all of NATO on similar platforms — by replacing old Soviet-era jets with Western ones, particularly the F-16 and in some cases, the F-35 — has gained momentum.

Some of the NATO countries are now rethinking tying their defense to U.S.-made systems and potentially considering European jets.

Angering an F-35 partner

In Canada, where Trump has launched a trade war and has threatened economic coercion to make it the 51st American state, new Prime Minister Mark Carney has asked Defense Minister Bill Blair to review its purchase of F-35s. Canada has been a partner with the U.S. in developing the fighter.

Blair will see if there are other options “given the changing environment,” a defense spokesman said.

Carney on Tuesday announced an early warning radar system purchase from Australia worth Canadian $6 billion ($4.2 billion). Officials say it will have a smaller footprint than a similar American system.

And in Portugal, the outgoing defense minister recently told a Portuguese newspaper that “recent positions” taken by Washington compelled a rethink about the purchase of F-35s. Portugal is considering various options to replace its F-16s.

“You’re not just buying an airplane, you’re buying a relationship with the United States,” said Winslow T. Wheeler, who spent three decades in U.S. Congress working for Democrats and Republicans on national security and defense issues. “People in the past have not just welcomed, but craved that kind of relationship.”

The Netherlands and Norway, on the other hand, have recently voiced support for the F-35 program.

The F-35 and a ‘kill switch’

The F-35 Joint Strike Fighter was designed to combine stealth, maneuverability and attack capabilities in a single aircraft. Each jet costs about $85 million (78 million euros), and the price jumps to as high as $150 million (137 million euros) when supporting infrastructure and spare parts are included.

About 1,100 have been produced to date for 16 military services across the globe.

The F-35B, a variant that can take off from ship decks vertically, is the latest model. It’s the most expensive weapons system the U.S. has ever produced, with estimated lifetime costs now expected to top $1.7 trillion. One of the ways the program was counting on reducing those costs was by selling more aircraft to international customers.

But the Trump administration’s recent stance on the Russia-Ukraine war has fueled fears that Washington may have similar ways to coerce buyers in a future fight — such as by embedding a hypothetical “kill switch” in the F-35’s millions of lines of programming.

The Pentagon’s F-35 Lightning II Joint Program Office, however, vehemently rejected that notion.

“There is no kill switch,” the office said in a statement on Tuesday. “We remain committed to providing all users with the full functionality and support they require.”

But that’s not the only way to impact an ally’s program, Wheeler said. The F-35 requires constant U.S.-controlled tech upgrades to operate in combat. If a relationship with the U.S. soured and updates were delayed, it could make a jet, or even a fleet, inoperable, he said.

Lockheed Martin said in a statement on Tuesday that the defense contractor delivers “all system infrastructure and data required for all F-35 customers to sustain the aircraft.”

European jet alternatives

The Saab Gripen, Eurofighter Typhoon and Dassault Rafale could see an increase in sales if other countries decide to forgo their F-35 purchases. But none of them have the F-35’s stealth capabilities.

The Swedish-made Saab Gripen is used by the militaries of Sweden, the Czech Republic, Hungary, South Africa,Brazil and Thailand. Conventional defense industry wisdom says it’s significantly cheaper than the F-35, Wheeler said.

The Eurofighter Typhoon, part of the British, German, Spanish and Italian forces, is manufactured by a consortium of defense companies: Airbus, BAE Systems and Leonardo.

The French-built Dassault Rafale twin-jet fighter is used by some branches of France’s armed forces. The governments of Egypt, India, Qatar, Greece, Croatia, the United Arab Emirates, Serbia and Indonesia have all signed contracts for Rafales.

David Jordan, a senior lecturer in defense studies at King’s College London and co-director of the Freeman Air and Space Institute, said that previously, European leaders felt it was easier and more cost-effective to lean on the U.S. defense industry to get access to advanced weaponry.

But the Trump administration’s move away from Europe could be the turning point, Jordan said.

It would require the continent to pool its money and resources — often a sticking point among the countries — into research and development, manufacturing and logistics.

But “the European defense industry is more than capable of building what it needs” within a decade, Jordan said.

French President Emmanuel Macron is already ramping up his efforts to persuade allies to switch to European defense contractors and weapons systems, including being offered Rafale fighters over F-35s.

If the Europeans increase their production, it would greatly affect the bottom lines of Lockheed Martin and other U.S. defense companies. Jordan said that U.S. defense contractors are likely concerned about Trump’s next move.

“At what point will they say ‘we don’t like this, we’re talking about risking billions of dollars here,’” Jordan said.

The White House didn’t respond to a request for comment on Tuesday.