Former U.S. President Donald Trump on Saturday said he would encourage Russia to do 鈥渨hatever the hell they want鈥 to any NATO member country that doesn鈥檛 meet spending guidelines on defense in a stunning admission he would not abide by the collective-defense clause at the heart of the alliance if reelected.

鈥淣ATO was busted until I came along,鈥 Trump said at a rally in Conway, South Carolina. 鈥淚 said, 鈥楨verybody鈥檚 gonna pay.鈥 They said, 鈥榃ell, if we don鈥檛 pay, are you still going to protect us?鈥 I said, 鈥楢bsolutely not.鈥 They couldn鈥檛 believe the answer.鈥

Trump said 鈥渙ne of the presidents of a big country鈥 at one point asked him whether the US would still defend the country if they were invaded by Russia even if they 鈥渄on鈥檛 pay.鈥

鈥淣o, I would not protect you,鈥 Trump recalled telling that president. 鈥淚n fact, I would encourage them to do whatever the hell they want. You got to pay. You got to pay your bills.鈥

The White House later Saturday called Trump鈥檚 remarks 鈥渁ppalling and unhinged鈥 and touted President Joe Biden鈥檚 efforts to bolster the alliance.

鈥淧resident Biden has restored our alliances and made us stronger in the world because he knows every commander in chief鈥檚 first responsibility is to keep the American people safe and hold true to the values that unite us. 鈥 Encouraging invasions of our closest allies by murderous regimes is appalling and unhinged 鈥 and it endangers American national security, global stability, and our economy at home,鈥 White House spokesperson Andrew Bates said in a statement.

NATO Secretary General Jens Stoltenberg said Sunday that Trump鈥檚 comments about the alliance put European and American soldiers at risk.

鈥淎ny attack on NATO will be met with a united and forceful response,鈥 Stoltenberg said in a statement. 鈥淎ny 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.鈥

European Council President Charles Michel on Sunday described comments from Trump on NATO 鈥渞eckless,鈥 adding they 鈥渟erve only Putin鈥檚 interest.鈥

鈥淩eckless statements on NATO鈥檚 security and Art 5 solidarity serve only Putin鈥檚 interest. They do not bring more security or peace to the world,鈥 Michel said in a post on X. 鈥淭he Transatlantic Alliance has underpinned the security and the prosperity of Americans, Canadians and Europeans for 75 years.鈥

At the core of the North Atlantic Treaty Organization and enshrined in Article 5 of the treaty is the promise of collective defense 鈥 that an attack on one member nation is an attack on all the nations in the alliance. Trump has long complained about the amount other countries in NATO spend on defense compared with the United States and has repeatedly threatened to withdraw the US from NATO. But his comments Saturday are his most direct indication he does not intend to defend NATO allies from Russian attack if he is reelected.

Trump has for years inaccurately described how NATO funding works. NATO has a target that each member country spends a minimum of 2% of gross domestic product on defense, and most countries are not meeting that target. But the figure is a guideline and not a binding contract, nor does it create 鈥渂ills鈥; member countries haven鈥檛 been failing to pay their share of NATO鈥檚 common budget to run the organization.

Republican Sen. Marco Rubio, who has endorsed Trump, said Sunday he had 鈥渮ero concerns鈥 about the former president鈥檚 NATO comments.

Rubio told CNN鈥檚 Jake Tapper on 鈥淪tate of the Union鈥 that Trump was merely reflecting on an anecdote from his presidency, arguing member nations weren鈥檛 鈥減aying their dues鈥 until Trump 鈥渦sed leverage鈥 to push NATO countries to 鈥渟tep up to the plate.鈥

鈥淭rump鈥檚 just the first one to express it in these terms,鈥 the Florida Republican said.

As president, Trump privately threatened multiple times to withdraw the United States from NATO, . Trump has described NATO as 鈥渙bsolete鈥 and has aligned himself with Russian President Vladimir Putin, who wants to weaken the alliance. Trump has long praised Putin and went as far as to side with the Russian leader over the U.S. intelligence community over Russia鈥檚 interference in the 2016 presidential election.

This story has been updated with additional developments.

CNN鈥檚 Kaanita Iyer, Daniel Dale, Marshall Cohen, Veronica Stracqualursi, Jim Acosta, Kevin Liptak and Martin Goillandeau contributed to this report.