SpaceX and Tesla CEO Elon Musk criticized acting NASA Administrator Sean Duffy after he told media outlets this week that the billionaire's space company is falling behind U.S. plans to return to the moon.

"The person responsible for America's space program can't have a 2 digit IQ," Musk wrote in a Tuesday post on X.

In response to other user posts, Musk referred to the Transportation secretary as " *Sean Dummy " and said he is " trying to kill NASA! " Musk later posted a poll asking users "Should someone whose biggest claim to fame is climbing trees be running America's space program?" Musk appeared to be referring to Duffy's background as a competitive speed climber.

On Monday, Duffy told CNBC that SpaceX was "behind" schedule on building its lunar landing system

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