Former President Trump’s potential reelection is raising fears at home and in Europe that he could put transatlantic alliances in the crosshairs, perhaps even pull out of NATO, as well as upend American support for the war in Ukraine.

Trump is the near-certain GOP presidential nominee, and polls show him leading President Biden nationally and in swing states. 

With the U.S. and NATO members heavily invested in protecting Ukraine and maintaining alliances, Congress passed legislation in December barring the president from unilaterally withdrawing from NATO without a two-thirds approval from the Senate. But this has done little to calm those nervous about a second term for Trump, who railed against the organization in his first term.

“The fact that the Senate felt necessary to include such a provision in the National Defense Authorization Act (NDAA) is disconcerting enough,” said one European diplomat, who requested anonymity to discuss a sensitive issue. 

“Our reading of the NATO withdrawal section is that if it gets tested, the president will prevail.”

John Bolton, who served as national security adviser to Trump but views him as dangerous for the country, said he is “convinced” Trump would pull out of NATO if elected. 

“I think this is something he feels strongly about. He thinks the Europeans still aren’t paying their fair share, he thinks they have negotiated very negative trade deals with us, I think he’s looking forward to getting out of NATO,” Bolton said in an interview with MSNBC last month.

Ivo Daalder, who served as ambassador to NATO during the Obama administration, said Trump can take a host of actions undermining the security of NATO without officially withdrawing from the alliance, and the provision in the NDAA does little to prevent such actions. 

“I don’t put a lot of money on the legislation,” he said.

“I think it’s important as an indicator that Congress overwhelmingly supports U.S. membership in NATO and that is to be welcomed, but it doesn’t prevent the United States from reducing, if not completely eliminating, its commitment to NATO.”

The actions Trump — or any leader antagonistic towards NATO and Europe — could take range from frustrating work in Brussels by instructing U.S. diplomats to skip meetings, attend and stay silent, grandstand or vote against measures requiring consensus. All these things could bring the body to a standstill. 

The U.S. could refuse to participate in planning sessions or NATO military exercises, or refuse to share intelligence with NATO members.

Also concerning is how the U.S. would respond to a potential Article 5 request — the mutual defense provision that any NATO member can invoke if attacked. It is viewed as the strongest deterrent against any aggression, in particular by Russian President Vladimir Putin. 

On the campaign trail, Trump has bragged that as president, he threatened to hold back America’s commitment to Article 5 because some member states had not met their financial obligations. 

“And I went to ’em and I said, ‘If you don’t pay, we’re not going to protect you.’ And they said, ‘Do you mean that?’ I said, ‘I mean that,’” Trump said in an interview with Fox News in January. 

Daalder, who is president of the Chicago Council on Global Affairs, said Trump could instruct his representative to vote against invoking Article 5 at NATO, removing any legal obligation to respond to the mutual defense pact. If the U.S. voted in favor, Trump could still hold back American military support, pointing to the treaty text that each country can provide assistance “as it deems necessary.”

“Trump may say, Well I’m going to send a minesweeper, that’s my contribution you guys figure it out.”

Europeans and NATO Secretary-General Jens Stoltenberg have pushed back on claims that Europe and NATO members are not pulling their weight, contributing enough to the alliance or supporting Ukraine. 

“Since the outbreak of the war, the United States has provided around 75 billion U.S. dollars. Other Allies and partners have provided over $100 billion,” Stoltenberg said late last month during a speech at the Heritage Foundation.

The conservative Washington think tank is a home for national security professionals who served in Trump’s first term in office and could staff a potential second administration. 

Stoltenberg, during a panel discussion, pushed back on an assertion by Trump’s former deputy national security adviser Victoria Coates that Putin’s full-scale invasion of Ukraine pointed to a failure of NATO’s deterrence.

“NATO’s deterrence is about Article 5. And that applies for NATO allies — that has never failed,” he said. 

“Ukraine is a partner, but Ukraine is not covered by Article 5. So I think we should not confuse those two things because then we are actually undermining the credibility of Article 5.”

Still, Stoltenberg’s remarks to Heritage, to a crowd supportive of Trump’s confrontational and transactional approach to policy, sought to sell the alliance as a “good deal” for the U.S.

“Over the last two years, NATO allies have agreed to purchase $120 billion worth of weapons from U.S. defense companies,” Stoltenberg said. 

“American jobs depend on American sales to defense markets in Europe and Canada.”

Robert Greenway, director of the Heritage Foundation’s Center for National Security, said a second-term Trump would likely not back away from holding a strong leadership position in NATO, but that it would “look a little bit different,” and he repeated criticisms that European allies need to step up more on defense spending. 

“I think just the fear, or the anxiety perhaps with Trump’s return, or potential return to the White House, I think has some countries revisiting their security commitments to their own security, let alone NATO. I think that’s probably also a healthy thing,” he said about conversations with colleagues in Europe.

“But we tell them, at the end of the day, that we don’t envision circumstances in which a future President Trump would withdraw from NATO. I just don’t see the circumstances. I don’t see the desire to do that. But I do see the strong desire to get NATO to do more.”

But Europeans are angry about the narrative from Trump and his allies in Congress that Europe is shortchanging assistance to NATO or Ukraine, and that the U.S. is shouldering the burden. 

“When some Republican congressman and senator says ‘you need to do more’ — well, we’re giving everything we have, so we cannot actually do that much more,” Michael Aastrup Jensen, chairman of the Foreign Policy Committee for the Danish parliament, said after meetings on Capitol Hill this week.  

Denmark is one of five European countries that have committed 1 percent or more of their GDP to Ukraine, compared to the U.S., which has provided 0.3 percent, according to the Ukraine aid tracker by the Kiel Institute. 

Jensen was in Washington, along with his counterparts from Estonia, Iceland, Latvia, Lithuania, Norway and Sweden, lobbying for Congress to pass President Biden’s request for $60 billion in aid for Ukraine — the majority of that funding earmarked for U.S. defense production to backfill weapons that were sent to Ukraine. 

All the countries are NATO members — although Sweden is waiting on Hungary to ratify its accession to the alliance — and the group came with a dire warning that Europe can not sustain Ukraine’s defense against Russia without the U.S. 

Failure to defeat Russia in Ukraine would mean a war against NATO, they warned. 

“We’re at a place right now that Europe, even though we’re giving our fair share and then some to Ukraine, both when it comes to weapon systems and money, we are not able to fill the gap if the U.S. pulls out,” said Ine Eriksen Søreide, chair of Norway’s foreign policy committee in parliament.

“And that’s not about money, it’s first and foremost about military equipment.”

When asked whether a second Trump administration — or Republicans in general — could be trusted to work with Europe, the Latvian chair of the foreign policy committee, Rihards Kols, said they have no choice. 

“We’re not privileged with which U.S. president we’re going to work [with]. Whoever U.S. citizens select as the next president, we are going to work.”

But Kols said he was pessimistic about Washington’s commitments. 

“The debate right now in Latvian society is actually in the direction, we are preparing for a war,” he said.

“That should be echoed here in the U.S. It’s taken very, very seriously.”