Trump was rebuked from all sides after saying in a speech Saturday that he would "encourage" Russia to attack members of NATO who had not met their financial obligations, in his most extreme broadside against the organization.

"I MADE NATO STRONG, and even the RINOS and Radical Left Democrats admit that," Trump said on Truth Social Monday, using an acronym deployed by conservatives for critics within their own party: Republicans in Name Only.

"When I told the 20 Countries that weren't paying their fair share that they had to PAY UP, and said without doing that you will not have US Military Protection, the money came rolling in. After so many years of the United States picking up the tab, it was a beautiful sight to see."

Trump has long complained about NATO, accusing Western allies of being freeloaders that do not pull their weight on military spending, taking for granted that they can rely on the US as a defensive shield.

But he demonstrated repeatedly both during and after his time in office that he either doesn't understand how NATO works or is unwilling to speak accurately about it.

In 2006, NATO countries made a vague commitment -- formalized in 2014 -- to spend two percent of their gross domestic product on their own defense, but members do not pay subscription fees and do not "owe" the alliance money for defense.

The two percent benchmark is voluntary and there are no penalties enshrined in NATO's founding treaty for falling short.

Speaking at a campaign rally in South Carolina on Saturday, Trump had described what he said was a conversation with a fellow head of state at an unspecified NATO meeting.

"One of the presidents of a big country stood up and said, 'Well, sir, if we don't pay, and we're attacked by Russia, will you protect us?' I said, 'You didn't pay, you're delinquent? No, I would not protect you,'" Trump told his supporters.

"In fact, I would encourage them to do whatever the hell they want."

President Joe Biden slammed the comments as "appalling and dangerous," warning that his predecessor, who is running for reelection, intended to give Russian leader Vladimir Putin "a greenlight for more war and violence."

Trump's remarks came after Senate Republicans last week rejected a bipartisan bill that would have included $60 billion in funding for Ukraine, plus aid for ally Israel, along with reforms to address the US-Mexico border crisis.

A foreign aid package that includes the Kyiv support but decouples the funding from the border issue entirely passed a key procedural vote in the US Senate on Sunday, though Republicans are still expected to block it from becoming law.