SpaceX CEO Elon Musk suggested Transportation Secretary Sean Duffy was not smart enough to lead NASA after he threatened to pull a moon landing contract from the billionaire's rocket company.

On Tuesday, Musk responded to a comment on X that criticized Duffy for his dual role as transportation secretary and NASA administrator.

"Duffy, wanting to kill NASA's role as an independent agency, seems to be a particularly bad choice at the moment," the commenter noted.

"The person responsible for America's space program can't have a 2 digit IQ," Musk replied.

The attack on Duffy came just a day after he told CNBC that NASA would modify or cancel SpaceX's contract to land astronauts on the moon in the coming years.

"They push their timelines out, and we're in a race against China," Duffy said. "So, I'm going to open up the contract. I'm going to let other space companies compete with SpaceX."

In 2021, NASA chose Musk's Starship as the vehicle to land astronauts on the moon, but it has seen recent setbacks, including three in-flight failures this year.