Trump's comments came during a weekend rally in South Carolina in which he appeared to recount a meeting with NATO leaders.
The former president - and likely 2024 Republican nominee - claimed that the president of a "big country", whom he did not name, once asked him about potential U.S. protection from Russia if that nation fell short on its defense spending.
Trump said he told the NATO leader that the U.S. in that case would offer no protection, and went as far as to say he would even encourage Russia to (quote) "do whatever the hell they want."
NATO's 31 members have agreed on a target of defense spending that is at least 2% of each country's gross domestic product. Estimates have shown that only 11 member nations are spending that much.
In a written statement on Sunday, NATO Secretary General Jens Stoltenberg responded to Trump's comments by saying (quote) "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."
Poland's Defense Minister also weighed in, posting on social media, (quote) "NATO's motto 'one for all, all for one' is a concrete commitment" adding that "No election campaign is an excuse for playing with the security of the Alliance."
EU Internal Market Commissioner Thierry Breton, in a televised interview in France, said Trump may have (quote) "issues with his memory" - Breton recalling that Trump actually had his conversation with European Commission President Ursula Von der Leyen, and not a male president of a NATO country as Trump had relayed.
Meanwhile, the White House had its own response, with spokesperson Andrew Bates calling Trump's comments (quote) "appalling and unhinged."
