When Donald Trump suggested during the 2016 presidential campaign that he might not honor a U.S. commitment to defend other NATO countries if they were attacked, it triggered alarm throughout the trans-Atlantic alliance.

With Trump’s “America First” rhetoric drawing cheers from fervent supporters, the future of the North Atlantic Treaty Organization is once again on the agenda. But this time, European leaders acknowledge the alliance must evolve to meet the challenges of the 21st century and say they are ready to shoulder more responsibility for their own defense.

A lot has changed in eight years.

First, Trump’s presidency forced Europe to recognize that U.S. military support was no longer guaranteed, then Russia’s invasion of Ukraine underscored the threat on its eastern border. Meanwhile, the U.S. has increasingly focused on China’s expansion in the Asia-Pacific, as well as Iran and North Korea.

“Confronted with powers such as Russia and China, and a United States whose pivot to Asia seems inevitable, no matter who wins the next election, we Europeans need to do more to ensure our own security,” Josep Borrell, the European Union’s foreign policy chief, wrote last weekend in The Times of London.

After relying on U.S. leadership of NATO to protect them with overwhelming nuclear and conventional capability for the past 75 years, European nations must take on a larger role in funding and leading the 32-nation alliance because their interests are increasingly diverging from those of the United States.

“We are talking about a NATO which the United States is still part of, but which the United States is no longer the indispensable leader (of),” said Malcolm Chalmers, deputy director-general of the Royal United Services Institute, a London-based think tank focused on defense and security. “I mean, that is what JD Vance and Donald Trump are talking about. They’re talking about a NATO that is transformed and one in which the Europeans take the greatest share of the burden.”

NATO grew out of secret talks among U.S. officials after World War II about how to supply military equipment to Western Europe and ensure a coordinated response to any attack by the Soviet Union. The 12 founding members signed the North Atlantic Treaty on April 4, 1949.

NATO’s military structure is headed by the Supreme Allied Commander Europe, who is also the commander-in-chief of American forces in Europe. The U.S. is expected to spend almost twice as much on its military this year as all the other alliance members combined, according to NATO statistics.

Trump’s skepticism about NATO was underlined last week when he named Vance as his running mate. Vance has opposed U.S. support for Ukraine, has criticized European nations for slashing defense spending since the Cold War, and said it’s time for “Europe to stand on its own feet.”

Europe got another wakeup call on Sunday when President Joe Biden, whose strong support for NATO was cemented during standoffs with the Soviet Union in the 1970s, said he would not seek reelection. Vice President Kamala Harris, the likely Democratic presidential nominee, has backed the administration’s position on NATO and aid to Ukraine, but she entered politics long after the Cold War and is better known for her work on domestic issues.

“The question is whether she will have that same strong trans-Atlantic view that’s kind of part of her blood in the way that Biden had it,” said Armida van Rij, an expert on European security policy at the Chatham House think tank in London.

Trump’s threat to renege on NATO’s collective security guarantee, a cornerstone of the alliance, is based on his belief that member states aren’t living up to their funding commitments, forcing U.S. taxpayers to subsidize Europe’s defense.

That argument has weakened since 2016.

Twenty-three of the alliance’s 31 non-U.S. members will meet or exceed their commitment to spend at least 2% of economic output on defense this year, up from just three 10 years ago, according to figures compiled by NATO. Overall, the non-U.S. members now spend 2.02% of gross domestic product on defense, compared with 3.4% by the U.S.

Besides that, the European Union has ambitious plans to boost its defense industry in response to the threat posed by Russia’s war on Ukraine. France’s President Emmanuel Macron has urged European nations to seek more independence on airspace defense and relocate production to the continent rather than purchasing material off the shelf from American arms merchants.

The EU plans center on streamlining arms procurement and to increasingly produce them within the 27-state bloc in a multibillion-dollar pivot away from the United States.

The risks for Europe, as well as the United States, are evolving. It’s not just about Russian tanks on Europe’s borders. NATO, as a defensive alliance, must also consider the threats posed by Iran, China and North Korea and be prepared for cyber warfare and foreign interference in elections, as well as conventional military attacks, van Rij said.

That means European nations need to increase troop numbers, upgrade equipment such as tanks, fighter planes and transport aircraft, and improve their ability to counter technological threats, she said.

“We need to look at this not as Trump-proofing, but as future-proofing European security and the NATO alliance as a whole,’’ van Rij said. “Because yes, while there are concerns about U.S. engagements in Europe … — and the JD Vance appointment as Trump’s running mate has only accelerated concerns — there is a bipartisan focus on China, which in the medium- to longer-term could mean that we see resources being reallocated elsewhere.’’

One model may be NATO’s newest members, Finland and Sweden, which joined the alliance to bolster their security in the face of Russian aggression.

As historically non-aligned nations, they were forced to develop strategies to fight off any Russian incursion largely on their own, equipping their militaries with a full range of capabilities sometimes missing in NATO countries that are used to relying on the U.S. for commanders and battle plans. Both have military service, important weapons industries and large standing armies.

“The Finnish defense people would say … we planned up to now to fight Russia by ourselves, now NATO is definitely a bonus…,’’ Chalmers said. “NATO countries have the opposite problem. They’re so used to thinking about fighting with others and particularly fighting with the Americans, they sometimes get out of the habit of thinking about fighting for themselves.”

The risks of over-reliance on the U.S. were highlighted this year when the House of Representatives blocked $61 billion of military aid for Ukraine for months while conservative Republicans argued the government should focus on domestic border security and the nation’s rising debt.

While the funding was eventually approved, the delay left Ukraine short of ammunition and hardware as Russia launched a brutal spring offensive.

A second Trump presidency would bring that mindset to the White House.

“Today … we peer apprehensively across the Atlantic at a worst case in which an erratic, ignorant, self-obsessed prospective U.S. president might cut us loose,’’ historian Max Hastings wrote in The Times. “Trump is right about one big thing: behind an American shield, since the 1950s Europeans have enjoyed an almost free ride. This is now over, and Vladimir Putin is licking his lips.’’

(AP)