Several developments in the U.S. presidential race, including former President Donald Trump’s pick of JD Vance as vice president earlier this month, have left European NATO member countries worried as they contemplate the possibility of the U.S. reducing its leadership role in the treaty organization — or pulling out altogether — analysts say.

American presidents from both parties have long criticized a lack of burden sharing within NATO, pointing to many countries not matching the 2% of GDP defense spending commitment. With the upcoming U.S. presidential election and Trump and Vance’s criticisms of the alliance, NATO’s future is effectively on the ballot , some foreign policy experts say.

Trump has frequently criticized NATO countries for placing a financial burden on the U.S., warning that if they do not increase their contributions, he might consider reducing America’s involvement in the alliance or withdrawing completely.

“NATO has to treat the U.S. fairly, because if it’s not for the United States, NATO literally doesn’t even exist,” Trump said in a March interview .

The U.S. spent 3.49% of its GDP on defense in 2023, while 19 of 32 NATO countries failed to reach the 2% commitment . This year, 23 out of 32 countries are expected to meet or exceed the defense-spending target, according to NATO.

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Embracing Trump’s “America First” foreign policy platform, Trump and Vance favor isolationism. This raises the question: What does this mean for NATO member countries in need of American assistance, especially Ukraine and neighboring countries around Russia?

Even if Vice President Kamala Harris — the anticipated Democratic presidential nominee — wins the election in November, NATO may still face challenges.

A Trump and Vance ticket

Klaus Larres, a history professor at the University of North Carolina and a fellow at the Wilson Center, noted that not all campaign rhetoric translates into actions once in office.

Trump is more skeptical of NATO than President Joe Biden’s administration, but since more countries are meeting the defense spending commitment, that grievance may diminish, Larres said.

“He probably will not repeat again that he wants to leave NATO, but he probably will make the United States less active in NATO and less prominent and less being the clear leader of NATO,” he said.

Larres said Vance’s inexperience in foreign policy will require a steep learning curve, which could prompt him to reconsider his instinctive isolationism.

“He is an isolationist, and he wants to withdraw from Ukraine,” Larres said. “He doesn’t seem to see how detrimental that also would be for the United States and not just for the Europeans or for Ukraine, that it would have really devastating effects on America’s role in the world. He doesn’t seem to understand that.”

With 40% of global trade involving the U.S. and Europe, a serious strain in relations would harm America not only in security but also in trade and economic policy, Larres said.

A Harris ticket

Harris is expected to be the Democratic presidential nominee, following Biden’s announcement that he won’t seek reelection. Harris, who as of this writing has not announced a vice presidential candidate, will face a formal nomination at the Democratic National Convention in August.

During his presidency, Biden expanded and defended NATO while bringing the Atlantic allies closer together, Larres said. Foreign policy experts expect Harris to continue support for NATO and Ukraine.

In contrast to the Republican ticket, Harris has indicated she would not stray from NATO.

“I firmly believe our commitment to build and sustain alliances has helped America become the most powerful and prosperous country in the world — alliances that have prevented wars, defended freedom and maintained stability from Europe to the Indo-Pacific,” Harris said at the Munich Security Conference in February.

“To put all of that at risk would be foolish,” Harris said.

In a February rally, Trump said he would encourage Russia to do “whatever the hell they want” to any NATO country that doesn’t meet the defense spending commitment.

In response, Harris criticized Trump’s remarks and reaffirmed her opposition to Russian President Vladimir Putin and the war in Ukraine.

“No previous U.S. president, regardless of party, has bowed down to a Russian dictator before,” Harris said in an interview .

In the days leading up to Russia’s invasion of Ukraine in 2022, Harris urged NATO countries to unite and prepare sanctions.

During her Munich speech, Harris warned against American isolationism, stating abandoning Ukraine or NATO allies would repeat historical mistakes.

“If we stand by while an aggressor invades its neighbor with impunity, they will keep going,” she said, noting Putin’s actions could threaten all of Europe.

“If we fail to impose severe consequences on Russia, other authoritarians across the globe would be emboldened, because you see, they will be watching — they are watching and drawing lessons.”

The ‘bedrock’ of NATO

Foreign policy experts warned diminishing America’s involvement in NATO could signal to adversaries abroad they can take advantage of U.S. allies, as America’s military strength is a key deterrent.

Elizabeth Saunders, a professor of political science at Columbia University and a nonresident senior fellow at the Brookings Institution, said the U.S. military is the “bedrock” of NATO, and the U.S. nuclear program is still a key part of how NATO deters adversaries, like Russia.

“It’s very clear that this dance that NATO countries and Russia are doing on the sort of outer edges of this conflict are designed to prevent direct hostilities between any NATO country and Russia, and that’s why Ukraine rightly believes that its security is tied to whether or not because it can get into NATO,” Saunders said.

On his campaign website, Trump argued “we have to finish the process we began under my Administration of fundamentally reevaluating NATO’s purpose and NATO’s mission,” claiming Russia is not the greatest threat to the U.S.

“You don’t have to believe that Russia is the greatest threat to the U.S. to think that it is a threat to U.S. interests,” Saunders said.

Hans Binnendijk, a fellow at the Atlantic Council’s Scowcroft Center for Strategy and Security and an adjunct political scientist at the RAND Corporation, said the most acute risk to the U.S. is Russia because the war in Ukraine has the potential for escalation.

“So, if the alliance is significantly weakened, [Putin] may feel that he can take advantage of that and he goes into the Baltic states, for example, which would be very dangerous,” Binnendijk said.

Because NATO relies heavily on the U.S. for nuclear deterrence, undermining the alliance would weaken its effectiveness, Binnendijk said. As he sees it, the most immediate risk of a Trump and Vance win is Congress failing to agree on future aid for Ukraine. He noted delays in past aid bills have led to shortages of air defense and artillery munitions for Ukraine.

“If the U.S. just decides to stop aid to Ukraine, Europe can pick up some of it, but certainly not all of it, and it would probably force Ukraine into a very unfavorable situation where they might have to cut a really bad deal with Putin that would in turn do a lot of damage internally to the alliance,” he said.

Even if Trump doesn’t formally withdraw the U.S. from NATO, he could still reduce America’s involvement in ways that undermine the alliance and leave other member countries more vulnerable, Saunders said.

For example, Trump could refuse to appoint an ambassador to NATO or withdraw U.S. troops from allied countries, Saunders said.

“But if the fundamentals, if the material and the personnel and the capabilities that you need come from the U.S., then if you don’t have access to those, then you don’t really have NATO in its current form,” Saunders said. “You have something else that might still be called NATO.”