A wargame simulated a 2nd Trump presidency. It concluded NATO would collapse.

• Trump has threatened to quit NATO. A wargame examined the possible ramifications.

• The US player abandoned Ukraine and ceased NATO participation, triggering crisis in Europe.

• The game's designer says it showed Trump "doesn't need to leave NATO to ruin it."

If Donald Trump wins a second term in the White House in November, NATO may fall apart, a recent wargame found.

As a presidential candidate, Trump has threatened to quit NATO unless European allies contribute more, and should he carry it out Europe may decide to go it alone on defense, the game suggests. "A US policy of frustrating NATO has the potential to cause the alliance to collapse, with the EU as a candidate for eventually replacing NATO's ultimate function — defending Europe from Russia," wrote Finley Grimble, the British defense expert who designed and ran the game.

The US doesn't have to withdraw from NATO to imperil the 75-year-old alliance. Technically, the US is barred from leaving NATO after Congress voted in 2023 to prohibit withdrawal without congressional approval.

But the game showed how Trump — the presumptive Republican presidential nominee who said on the campaign trail that he'd encourage Russia to "do whatever the hell they want" with NATO allies who spend too little on their militaries — could undermine NATO simply by doing as little as possible to support the alliance. "What Donald Trump can do is just really hollow out what NATO does," Grimble told Business Insider. "He doesn't need to leave NATO to ruin it. He can ruin it from within."

Grimble, who has conducted wargames for the British government, conceived of this game after claims by former US National Security Adviser John Bolton that he talked then-President Trump out of withdrawing from NATO in 2018. He designed a tabletop simulation where the players — mostly British specialists in defense, intelligence and foreign policy — assumed the role of leaders of the 32 NATO nations, plus Ukraine and Russia; China was played by the umpires. The US was played by an American who "was trying to enter into the psyche of Trump, which was no easy task," Grimble recalled.

Trump, who faces criminal charges in four separate cases, has been criticized for sowing chaos in American politics. And chaos is exactly what happens in the game when the fictional Trump takes office in January 2025.

The new administration immediately attempts to broker a peace deal — without European help — between Ukraine and Russia. After the mediation fails, Trump slashes aid to Ukraine.

It is the first domino to fall. Trump then drastically reduces US participation in NATO, including redeployment of 50 percent of American military assets in Europe, where more than 100,000 US troops are based, to the Indo-Pacific theater. The Trump administration also institutes a new policy called "dormancy." This includes a variety of go-slow tactics, such as less US participation in NATO exercises. A particularly damaging move is to bar the Supreme Allied Commander Europe (SACEUR) — the second-highest military position in NATO, and always a US officer — from acting without prior consultation with Washington.

"Ultimately, SACEUR is answerable to the president of the United States," said Grimble. "So he [SACEUR] can start slowing things down, or prevent things from happening. The US can just take the funding from NATO programs and they will collapse."

As the game continued, the US complains that some NATO members are failing to meet the alliance's goal of 2 percent of each nation's GDP on defense (the real-life Trump recently urged 3 percent). The complaints are valid: by the end of the game in 2027, many members still hadn't reached the 2 percent goal. Interestingly, while the US minimizes its presence in NATO, it does continue bilateral defense cooperation with the NATO members bordering Russia, including Finland, Romania, Poland and the Baltic States.

NATO was created four years after the end of World War II in an attempt to avoid the failures of the interwar years. American security guarantees have precluded European powers from re-arming in exchange for the greater expenses borne by the US. But with this US security umbrella suddenly diminishing in the game, France and Germany call for the European Union to take over from NATO. This angers Poland, which saw this as an attempt by the French to kick the US out and to have France become the top military power in Europe.

Some NATO members also quail at the thought that they might actually have to fight Russia without support from America, the most powerful NATO member given the size of its conventional forces and nuclear arsenal. "If I'm Italy, for example, I'm certainly guaranteeing the security of Estonia," Grimble said. "But I'm not really expecting to have to play such a prominent and crucial role in this."

The Joint Expeditionary Force, a British-led military coalition of 10 Northern European nations that can operate independently of NATO, begins to make warfighting plans that assume there will be no NATO support. Turkey ponders whether to stay neutral —despite its NATO commitments — if Russia attacked the Baltic States.

Meanwhile, with its campaign in Ukraine stalemated, Russia mulls invading the Baltic States — which are NATO members — to take advantage of NATO disunity and perhaps split the alliance over willingness to risk war with Moscow. But the Russian player ultimately decides that Russia doesn't have the resources to fight Ukraine and occupy the Baltics — and invading NATO territory just might bring America back into the alliance.

However, fictional Moscow does launch new offensives in Ukraine. Bereft of US support — which Europe is unable to compensate for — Ukraine feels compelled to sign a peace that cedes eastern Ukraine to Russia and installs a pro-Russian government in Kyiv. Europe faces another problem: fear that Russia might attack NATO is scaring off domestic and international investors, causing European economies to stumble.

By the end of the game, the effects of a US pullback from NATO are global. China realizes that the US has really shifted its focus from Europe to the Pacific, which deters Beijing from invading Taiwan. Yet this doesn't reassure Japan, Australia and South Korea — US allies whose forces and bases are essential to efforts to counter China — which worry that Trump might change his mind and abandon them too. Iran becomes emboldened to assert its power in the Middle East, which spurs an arms race with Saudi Arabia.

All of which left the British frustrated. The UK has traditionally backed a transatlantic, America-Europe alliance rather than a purely European defense bloc. Yet in the game, it could neither persuade Trump to ease his demands, nor the European NATO members to spend more on defense. "The British felt, 'for God's sakes, Trump, give the Europeans some time,'" Grimble said. "But also, 'Europeans, please do something. Let's all come to an accord and keep NATO alive.'"

Wargaming experts always caution that games shouldn't be treated as predictors of the future, but only as experiments to explore possibilities. Nonetheless, this wargame seemed to confirm the worst fears of critics who believe Trump could destroy NATO and make Europe vulnerable to attack.

"The US had reduced its resourcing of the NATO deterrence and defense missions, meaning NATO did not have credible warfighting plans ready to deal with a Russian invasion," said Grimble. "The whole thing had become dysfunctional. It certainly wasn't in any position to coherently defend against Russia at the end of the game."

Yet at the same time, there was a genuine desire to keep NATO alive. "Many NATO members — except for France mainly — thought post-Trump it could be salvageable," Grimble said. "So it was necessary to keep the US in, keep it together, and rebuild later."

Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds an MA in political science from Rutgers Univ. Follow him on Twitter and LinkedIn.

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