The looming prospect of NATO-skeptic Donald Trump winning a second term as president of the United States is serving as food for thought in Europe on everything from climate to trade.

But this week, explosive comments from the isolationist front-runner to be the Republican Party's candidate for president have pushed concerns about security in the European Union to the fore and loomed large over a NATO defense ministers' meeting in Brussels on Thursday.

At a campaign rally on Saturday, Trump implied he wouldn't come to the aid of NATO states should Russia attack if they hadn't met the alliance's military spending targets.

In fact, he would have opted to "encourage" Russia "to do whatever the hell they want," he said, recounting a conversation he claimed to have had with the leader of an unnamed major European country while in office between 2016 and 2021.

Trump has long railed against European NATO allies that spend far less than Washington in both real and relative terms on their militaries, slamming them for free-riding on an international security order backed up by US clout.

Europe's reaction to Trump's NATO remarks

Trump is known for hyperbole and still a long way from the White House, but his words reverberated on the other side of the Atlantic. Such a threat flies in the face of the central promise of NATO, enshrined as Article 5 in its treaties: Allies must come to each others' aid in the case of a military attack.

On Wednesday, NATO Secretary General Jens Stoltenberg touted increased spending by European NATO allies — an increase of 11% in 2023, he told reporters at a press conference ahead of the meeting.

"The whole idea of NATO is that an attack on one ally will trigger the response from the whole alliance. And as long as we stand behind that message, together, we prevent any military attack on any ally," he stressed.

EU politicians are concerned that they may not be able to count on the US if President Joe Biden, a Democrat who strongly condemned Trump's comments, loses in November elections.

The fear extends to Washington's huge nuclear arsenal. Though the information is classified, experts estimated that the US had about 3,700 warheads last year, with around 100 bombs stationed at military bases in Germany, Belgium, the Netherlands, Italy and Turkey. After the departure of the United Kingdom from the EU, France is the only member state with its own nuclear weapons.

"Judging by recent comments from Donald Trump, we can't count on that anymore," European Parliament Vice President Katarina Barley told German newspaper Tagesspiegel last week.

Asked by Tagesspiegel whether the EU needed its own nuclear bombs — something widely regarded as a pipe dream (or indeed, for some, a nightmare) for now — the center-left Social Democrat replied: "On our way to a European army, this could also become a topic."

How likely is a 'eurobomb'?

Nuclear armaments are highly divisive in the EU. Austria, Ireland and Malta have all signed an outright ban on nuclear weapons. While some countries, like France, Romania and Poland, more strongly favor nuclear deterrence, public opinion has traditionally been largely against them in many states, even ones like Germany that host US nuclear weapons.

Nuclear weapons analyst and researcher Franziska Stärk told DW there were different options under discussion in Europe, none of them very convincing for her.

"Suggestions in the EU context range from the EU developing its own arsenal to France and the UK substantially bolstering their arsenals and somehow kind of ‘Europeanizing' launch authority," the researcher from the Peace Research and Security Policy at the University of Hamburg said.

"Personally, I'm highly critical of the feasibility of these suggestions," Stärk said. "First of all, because the EU is not famous for making foreign policy decisions easily. And I can hardly see how they can establish a chain of command for a presumably multinational nuclear force."

Nuclear weapons from France?

What is more likely, according to Tom Sauer of the University of Antwerp, is for France to somewhat "Europeanize" its nuclear capabilities: "The French already now say that if the security interests of Europe are in danger, our nuclear weapons may help … [French President Emmanuel] Macron said that and all previous presidents said that one way or another."

France got nuclear weapons in 1960, but the rest of the EU has traditionally been lukewarm, Sauer told DW. Nonetheless, politicians in Germany have at times come out in favor of cofinancing or increasing coordination over French nuclear weapons.

A French member of the European Parliament, Christophe Grudler, told DW on Wednesday that the EU should consider this option.

"The French nuclear arsenal is under French command, uniquely a French mandate," the center-right lawmaker stressed. "However, if there was cooperation looking at how we could work on technical assistance, develop the principle of cohesion in Europe … it's something that we should indeed pursue."

Sauer said he is skeptical that France is completely sincere in this regard, pointing out that all this would bring up a whole range of issues. Would Germany finance French weapons without having control over them? And would Paris be willing to relinquish complete control over its weapons in exchange for cash?

Nuclear deterrence: A dangerous debate

Sauer and Stärk were both very critical of the entire discussion. "Instead of talking about the eurobomb, we should talk about having a nuclear-weapon-free zone in Europe extending to Russia, if possible," Sauer said.

Stärk said she wished some of the politicians proposing nuclear options actually "thought about the global implications when we talk about the value of the nonproliferation regime, which is obviously put into question if Europe decided to actually nuclearize."

On Wednesday, German Defense Minister Boris Pistorius also sought to downplay the discussion. He even criticized fellow Social Democrat Barley for being among the first German politicians to raise the issue, saying: "In my opinion, that's not something you discuss publicly."

How seriously should Europe take Trump's comments?

Asked if European states needed to rethink nuclear deterrence in light of Trump's comments, Stoltenberg said Wednesday that the "NATO nuclear deterrent … has provided the ultimate security guarantees for NATO allies for decades."

"This is the arrangement we have together in NATO, with agreed procedures for command and control doctrines we are exercising together. And of course, this is the combination of US nuclear weapons in Europe, but also other NATO allies providing the planes, the infrastructure, the support," he said.

Earlier in the week in a separate statement, Stoltenberg downplayed Trump's comments. "I expect that regardless of who wins the presidential election the US will remain a strong and committed NATO ally," he said.

Sauer of the University of Antwerp argued that Trump's comments don't actually have much bearing on the actual likelihood of European NATO states being attacked by Russia. The analyst doesn't believe Russian President Vladimir Putin has the inclination or the ability to invade such countries, unlike Ukraine, which is outside NATO and the EU.

On X, formerly Twitter, Hans Kristersen of the Federation of American Scientists called for calm.

"There are two ways to undermine NATO security," Kristersen wrote on Wednesday. "One is for Trump to say something stupid (which he does all the time). The other is for Europe to overreact and say, 'We can no longer rely' on the US nuclear umbrella and need a eurobomb. It's exactly what Putin [and] Trump want to hear."

Edited by: Timothy Jones