• Sanders tweeted a demand that "the extremely wealthy pay their fair share" which set the world's wealthiest person into a frenzy on Twitter.
• Last week, Musk sold about $6.9 billion worth of stock. (As of Monday morning, Musk still holds more than 166 million shares in the company.) As his sell-off continues, Musk will face a potentially massive tax bill.

Tesla and SpaceX CEO Elon Musk sparred with Senator Bernie Sanders over tax policy this weekend on Twitter, and tried to provoke him again on Monday morning.

According to his website, the independent Senator (who generally caucuses with Democrats) is a proponent of transitioning the U.S. energy system to renewables, providing $200 billion to a Green Climate Fund, and other environment-oriented policies that would serve Tesla well.

But he is also a proponent of hiking taxes for the super-rich, as is Oregon Democratic Senator Ron Wyden, who Musk needled on Twitter in a similar exchange earlier in November. Musk, who has the highest net worth in the world today, is staunchly against a so-called "billionaire's income tax."

Last week, Musk sold about $6.9 billion worth of stock. (As of Monday morning, Musk still holds more than 166 million shares in the company.) In recent weeks, sales from Musk and other insiders have put pressure on Tesla shares. Last week, Tesla stock declined 15.4%, marking the company's worst one-week performance in 20 months, and its worst week ever excluding declines in the first quarter of 2020 as the coronavirus pandemic sent markets tumbling. Tesla closed down another 1.94% on Monday.

As his sell-off continues, Musk will face a potentially massive tax bill. However, as ProPublica reported, Musk previously paid a 3.27% true tax rate, or $455 million, on wealth growth of $13.9 billion. Musk, who had an actual taxable income of $1.52 billion during the five-year period, paid no federal income taxes in 2018, according to ProPublica.

On Twitter, Sanders has amassed a following of more than 15 million, and Musk has amassed a following of 63.8 million.

The spat begins

On Saturday, the 80-year-old Vermont senator wrote in a tweet, "We must demand that the extremely wealthy pay their fair share. Period."

Musk replied the next day with, "I keep forgetting that you're still alive." Musk also asked Sanders on Sunday, "Want me to sell more stock, Bernie? Just say the word." Then, the CEO berated the senator saying, "Bernie is a taker, not a maker."

Musk attempted to engage Sanders once again on Monday.

He asked, "Ok, how much do you think is fair? Does 53% seem reasonable?"

When Sanders did not reply to him, a Musk fan remarked that the senator doesn't respond to followers on Twitter generally. Musk asked, "How do we know he hasn't been kidnapped by aliens!?" Musk continued to hold forth on Twitter, discussing his tax policy preferences with fans and followers including promoters of bitcoin and Tesla.

In his tweet exchanges, Musk revealed that he would support an estate tax, and taxes on what he called extravagant consumption.

The CEO also said he currently owns around 20% of Tesla's stock.

Sen. Sanders and Tesla did not immediately respond to requests for comments.

In 2020, Musk put his California mansions on the market while he was sparring with state health regulators over Covid-19 restrictions that impacted the Tesla factory in Fremont. He then moved to Austin, Texas, near the site of a new Tesla factory that's under construction.

This year, Tesla moved its headquarters from Palo Alto, California, to Austin, Texas, as well.

Moving from California, with the highest state income tax in the country, to Texas, which has no state income tax, could save Musk billions of dollars based on his compensation package awarded in 2018.