“I keep forgetting that you’re still alive,” Musk, the chief executive officer of Tesla and SpaceX, tweeted in a reply to the 80-year-old senator from Vermont. In a subsequent tweet, Musk asked: “Want me to sell more stock, Bernie? Just say the word…”

Musk offloaded almost $7 billion worth of Tesla stock over the past week, which helped to push the automaker’s shares down about 15% for the week. Musk’s stock sales began after he tweeted an unusual poll Nov. 7 on Twitter asking whether he should sell. 

Musk didn’t mention in his prior tweets that he had millions of stock options that must be exercised before they expire in August 2022. He said in September that he was likely to exercise “a huge block” of those options toward the end of 2021. Musk is worth about $286 billion as tracked on the Bloomberg Billionaires Index.

In October, Musk said Tesla would move its headquarters from California to Austin, Texas, a state which levies no income tax. On Saturday, Musk tweeted that he’s been living in a small home in South Texas for the past two years. “Feels more homey to live in a small house,” he wrote.

Sanders, a Vermont independent who caucuses with Democrats, chairs the Senate Budget Committee and has long advocated for the wealthy to pay more taxes. In March, Sanders tweeted that the amount of wealth accumulated by Musk and Amazon.com Inc. co-founder Jeff Bezos was “immoral.” Musk also recently chided U.S. Senator Ron Wyden, a Democrat from Oregon and chair of the Senate Finance Committee, who had pushed for a wealth tax on billionaires.