Elon Musk recently found himself in a tense exchange with a Danish astronaut after the latter criticized the tech mogul’s assertion that former President Joe Biden had deliberately left two American astronauts behind on the International Space Station.

On Thursday, Andreas “Andy” Mogensen posted a clip on X, featuring Musk alongside then-President Donald Trump. During this segment, Musk alleged that Nasa’s Butch Wilmore and Suni Williams had been abandoned on the space station for alleged “political reasons” by Biden, claiming the current administration was now intervening to rescue them.

Mogensen, a seasoned astronaut with two ISS missions under his belt—including a 2023 flight on a SpaceX Crew Dragon—responded sharply, stating, “What a lie. And from someone who complains about the honesty of the mainstream media.”

In retaliation, Musk called Mogensen “fully retarded,” asserting that “SpaceX could have brought them back several months ago” and mentioning that he had proposed this to the Biden administration, although he provided no details on what that proposition entailed.

Wilmore and Williams launched to the ISS in June aboard a Boeing Starliner, intended for a test mission lasting eight days to validate the new spacecraft. However, due to thruster issues, Nasa decided to send Starliner back without its crew and enlisted SpaceX to ensure the safe return of the experienced astronauts.

Nasa later confirmed that Wilmore and Williams would return on the SpaceX Crew-9 mission, which took off in September with a reduced crew of two to make space for the astronauts.

While the original return was slated for February, it has since been pushed to March due to delays in preparing the spacecraft for the upcoming Crew-10 mission, which will take over from Crew-9.

Musk has not disclosed any alternative rescue plans that might have been executed earlier.

In a conciliatory response to Musk’s comments, Mogensen expressed his admiration for Musk’s accomplishments, particularly at SpaceX and Tesla, stating, “You know as well as I do that Butch and Suni are returning with Crew-9, as planned since last September. Even now, you are not sending up a rescue ship to bring them home. They are returning on the Dragon capsule that has been on the ISS since last September.”