Palm Beach, Florida - Ex-President Donald Trump reacted angrily at the bombshell decision taken by the influential Americans for Prosperity (AFP) political network to endorse his rival Nikki Haley.

The organization founded by Republican megadonors David and Charles Koch announced on Tuesday that it was looking to "turn the page on today's toxic culture" by throwing its weight behind Trump's former ambassador to the UN.

Her surging numbers and popularity with supporters of other GOP presidential candidates put Haley in a strong position to "defeat Donald Trump," the AFP said.

The frontrunner for the Republican presidential nomination was never going to let that slide and on Wednesday went on the attack, dubbing the group "Americans for China Prosperity" in a raging Truth Social post.

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Squeezing another belittling nickname in there, Trump hit out at "Nikki 'Birdbrain' Haley" while claiming he was never interested in AFP's endorsement to begin with.

"These losers have fought me from 2016 to the present," he wrote. "They are bad for our Country, and so is a very weak and ineffective Birdbrain, who still says that 'President Trump was a GREAT President, I will never run against him.'"

Whether they have Haley or Florida Governor Ron DeSantis in second place, most Republican primary polls have Trump in the lead by close to or more than 50 points. The former president is facing 91 felony charges spread over four separate criminal indictments.