The Inspiration4 mission launched an all-civilian crew out of the Earth’s atmosphere last week, after which they orbited the planet for three days and then returned safely back to Earth on Saturday.
Mr Biden and the White House have so far not issued any statements on the landing, prompting Mr Musk to employ a turn of phrase used frequently by the Republican party and former president Donald Trump to mock the president.
“The President of the United States has refused to even acknowledge the 4 newest American astronauts who helped raise hundreds of millions of dollars for St Jude. What’s your theory on why that is?” asked a Twitter user.
“He’s still sleeping,” quipped Mr Musk.
The tweet drew sharp reactions from social media users. While some slammed the president, others came to his support for not immediately wishing the crew on their successful mission.
“Dude is busy running a nation during a pandemic. Post-war intelligence briefings. Cybersecurity threats. SCOTUS shenanigans and human rights. Budget and tax legislation,” wrote one user.
“Stroking the egos of billionaires isn’t a national priority.”
“Quite interesting to see Musk parroting Trump and directly attacking [the president]. He was on his advisory council, but still made you believe he’s generally impartial. Just to remind you: he made no similar snarky attacks on Trump or Xi Jinping. This is new,” wrote another user.
“You’re awake, you may be better than the sleeper. Why don’t you nominate yourself to be the next president of America instead of the sleeper?”
Others began attacking Mr Biden by using the hashtag #SleepyJoe.
“#SleepyJoe is sleeping. #Biden really is a failure,” wrote a user.
“Tweet of the day! #golden #SleepyJoe” wrote another.
Mr Trump has used the phrase “Sleepy Joe” to mock Mr Biden during the presidential campaign. This was one of the many nicknames he gave to his then rival presidential candidate.
More recently, Israel’s former prime minister Benjamin Netanyahu appeared to mock Mr Biden by repeating a previously debunked claim that he slept during a meeting with Israel’s newly elected prime minister Naftali Bennett.
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