He ‘is trying to kill NASA!’

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 for the space agency’s Artemis III mission and that he would consider other contracts with competitors such as Jeff Bezos’ Blue Origin.

SpaceX and Blue Origin will have until Oct. 29 to offer ways to speed up the project, a NASA official told CNBC. The agency will also ask the industry to suggest ways to “increase the cadence” of Moon missions.

President Donald Trump selected Duffy to become the acting NASA administrator in July. The position had been vacant since the start of Trump’s presidency. Trump had previously nominated Musk ally Jared Isaacman, but he pulled the nomination earlier this year, saying he was a “blue blooded Democrat, who had never contributed to a Republican before.”

CNBC reported earlier this month that Trump has held talks with Isaacman to reconsider the role.

NASA is racing against China and others to get humans back to the moon for the first time since 1972. The space agency launched the Artemis project under Trump’s first administration with the goal of creating a “long-term presence” on the moon for science and tech discovery.

SpaceX won a $2.9 billion contract to build the technology in 2021. Other contractors such as Blue Origin, Lockheed Martin and Boeing are participating in various stages of the program.

But the project has been fraught with setbacks.

NASA launched its first Artemis mission in November 2022. Last December, the agency delayed its planned Artemis missions. NASA’s first Artemis launch with astronauts is now slated for April 2026, with a third mission to land two astronauts on the moon planned for 2027.

Now, the space agency is also grappling with the aftershocks from an ongoing government shutdown that threatens to stall any plans to reopen contracts. NASA made exceptions for employees and contractors working on Artemis missions to keep working during the shutdown, CNBC previously reported.

When Musk worked at the helm of the so-called Department of Government Efficiency, NASA faced sweeping, anti-DEI-related reductions in force, and implemented deferred resignation programs that have slashed the space agency’s workforce.

Around 4,000 NASA employees accepted the deferred resignation program offers since Trump took office for his second term, which reduced the staff of the space agency by nearly one-fifth.

WATCH: Transportation Secretary Sean Duffy: SpaceX is behind Artemis III timeline

— CNBC’s Lora Kolodny contributed reporting.