Trump is threatening the very thing that gives NATO the strength to stand up to Russia

• Trump said he'd encourage Russia to do "whatever the hell they want" to NATO members who aren't meeting spending expectations.
• Trump has long expressed criticisms of the alliance, spurring anxiety among European partners.

While he was out on the campaign trail over the weekend, former US President Donald Trump told supporters he'd encourage Russia to do "whatever the hell they want" to the NATO members who aren't paying their fair share.

This sentiment isn't exactly new territory for Trump, who has long expressed a negative, distrustful view of NATO, but it is shockingly inflammatory, an open threat that the US won't hold up its end of the bargain and come to the aid of its allies should they be attacked.

More specifically, it's a threat to Article 5, the thing that gives the NATO alliance the strength to stand up to challenges like Russian aggression.

Amid the resulting backlash, his allies dismissed the remark as just Trump being Trump, or even praised its frank honesty. But few, if any, acknowledged what it shows: Trump, if reelected, doesn't need to remove the US from NATO to erode the binding trust that its members would defend one another should Russia attack.

On Saturday at a rally in South Carolina, Trump said he once threatened a fellow "large" NATO country who, he said, had declined to spend the 2% recommended equivalent of their GDP on NATO's collective defense but still wanted assurance that the US would help defend them should Russia attack.

"I said: 'You didn't pay? You're delinquent?' He said: 'Yes, let's say that happened.' No, I would not protect you. In fact, I would encourage them to do whatever the hell they want. You gotta pay," Trump said, referring to letting Russia do what it wanted.

Such a move would be an outright dismissal of Article 5, a major cornerstone of the alliance that guarantees that if any NATO ally were a victim of an attack, every other member would join together in their defense. This offers collective defense and collective deterrence against Russia.

Article 5 responses are not automatic and rely in part on political will and unwavering commitments from member nations to generate the desired effect.

It's not clear when, where, or even if this conversation Trump described took place. And like most of Trump's provocative and loud remarks, particularly on foreign policy, one questions whether they'll be reflected by his actual policy — or should even really be considered with any weight at all.

Regardless, his comments indicate a fundamental misunderstanding of how NATO works and how the US benefits from it.

There are not any dues in the alliance but rather expectations that members of the largest military bloc in history will continue to invest in its success to deter an aggressive Russia and empower it to respond to other threats and challenges.

And while the US may be the largest funder, it reaps many of the benefits. With NATO, the US is surrounded by a dozens of partners, defended by guaranteed allies should it go to war, and supported economically and geopolitically amid rising tensions with potential adversaries. America's unipolar moment has passed, and the importance of having friends can't be overstated.

It was a concept that Trump's former defense secretary, Jim Mattis, emphasized repeatedly, at one point telling NPR that "throughout history, we see nations with allies thrive, and nations without allies wither."

Article 5 has only been invoked once in the history of the alliance, and that was in the wake of the 9/11 terror attacks on the US.

Trump's latest remarks on NATO sparked anxieties in Europe and received significant criticism.

"Any suggestion that allies will not defend each other undermines all of our security, including that of the US, and puts American and European soldiers at increased risk," NATO Secretary General Jens Stoltenberg said Sunday, highlighting the good faith needed between NATO allies to uphold Article 5 — and how easily politics can poison critical trust. Trump stirred up feelings of uncertainty just with the mere suggestion the US wouldn't come to the aid of its allies.

During his one-term presidency, Trump regularly criticized the alliance, calling out fellow NATO members' spending on the defense budget and suggesting it wasn't a fair deal for the US. He even privately discussed pulling out of NATO several times, administration officials leaked to the press.

Reactions were volatile. Critics said the move would not only have destroyed over 70 years' worth of work and commitment from countless US policymakers and politicians but would have also given Russian President Vladimir Putin the ultimate gift of a severely weakened NATO.

There have been hurtles put in place to stop presidents from pulling out of NATO, but there are other ways to harm the alliance.

With Trump very likely to be the Republican Party's nominee for the presidential election this year, questions remain over whether he'll try to pick up where he left off.

In his comments on Sunday, Stoltenberg said he expected "that regardless of who wins the presidential election the US will remain a strong and committed NATO ally" before further stressing that any attack on a NATO member would be "met with a united and forceful response."

This discussion comes at a critical time for the alliance. NATO is facing a rather telling inflection point.

Many of its members continue to increase their defense spending and heavily invest in military support for Ukraine against Russia. For the most part, Russia's full-scale invasion in 2022 prompted the alliance to grow stronger and closer, much to Putin's dismay.

And just last April, it gained a new member, Finland, further strengthening it against Russia. Sweden's ascension may be close. And Ukraine has expressed keen interest in joining as soon as possible, although that process will likely have to wait until the end of the war.

For the most part, the majority of NATO seems more committed to the alliance's longevity and success than ever, but US commitments have been called into question lately as Republicans in Congress, with outside input from Trump, have hindered aid to Ukraine, forcing reassessments across Europe.

These developments make Trump's remarks even more concerning. Should he be reelected, it could take very little for him to instill anxiety in America's European allies and embolden Putin.