Elon Musk, the world’s wealthiest person, directed a series of insults at Bernie Sanders on Twitter after the U.S. senator repeated his call for billionaires to pay more in taxes.

Musk even raised the notion of selling more of his Tesla Inc. shares, which would require him to pay capital gains taxes.

The 80-year-old Sanders, who unsuccessfully sought the Democratic Party presidential nomination in 2016 and 2020, on Saturday tweeted that “we must demand that the extremely wealthy pay their fair share.” He didn’t mention Musk by name.