Elon Musk and Elizabeth Warren have traded criticisms over taxing the ultra-wealthy. Here are some of the most heated exchanges between the billionaire and the senator.

Musk, the CEO of Tesla and SpaceX, has an estimated net worth of $274 billion, according to the Bloomberg Billionaires Index. As CBS News reports, he became the first-ever person to have a net worth over $300 billion in the fall of 2021. He's taken to Twitter to poke fun at the fellow billionaire he displaced from the world's top spot — Jeff Bezos — replying to one of the former Amazon CEO's tweets with a silver medal emoji.

Bezos has been one target of Musk's rather infamous usage of Twitter. But while Musk has tweeted plenty at Bezos throughout their 15-year feud, his tweets also have the power to drive cryptocurrency, spark discourse, and, most recently, to vividly strike back at leading progressives in the Senate.

Over the summer, nonprofit news outlet ProPublica released a bombshell investigation into just how much America's wealthiest people pay in taxes. According to ProPublica's reporting, Musk saw his wealth grow by $14 billion from 2014 to 2018 — but he paid just $455 million in taxes.

And, in 2018, Musk paid no federal income tax, according to ProPublica. When the outlet attempted to reach him for comment, he responded with "?".

Lawmakers, including Sen. Elizabeth Warren, lept into action. Warren and Sen. Sheldon Whitehouse wrote a letter to Senate finance chairman Ron Wyden, saying that the committee should investigate the allegations that the report revealed by homing in on financial institutions and their role in tax avoidance.

"This tax avoidance by the nation's wealthiest individuals is profoundly unfair," Warren and Whitehouse wrote. "It leaves the nation unable to pay for critical investments in infrastructure, education, and health care. It favors investment income over wages, distorting our nation's economy and adding to inequality."

Warren also tweeted out the ProPublica report, calling out the finding that Musk paid no federal income tax in 2018. She wrote that it showed the need for a wealth tax.

Warren has been a longtime proponent for a wealth tax. It was a keystone of her presidential platform in her 2020 run, and she's since proposed legislation that would enact an ultramillionaire tax on households with a net worth of $50 million or more.

Musk has criticized a tax Democrats proposed on billionaires' unrealized gains — under which he'd owe an estimated $50 billion — writing on Twitter that "Eventually, they run out of other people's money and then they come for you."

After Musk was named person of the year by Time, Warren took to Musk's preferred medium of Twitter to spark action on the tax code. She said that it was time to "change the rigged tax code" so that the newly-named person of the year (and world's richest man) "will actually pay taxes and stop freeloading off everyone else."

Musk sent a few replies to Warren's tweet, telling her to "Stop projecting!" and linking to a Fox News report on her ancestry. He then said that Warren reminded him of a "friend's angry Mom" who would "just randomly yell at everyone for no reason."

Musk also went on to call Warren "Senator Karen."

He then returned to the thread later in the day to talk about just how much in taxes he would pay, saying he would pay more "than any American in history this year."

It's not the first time that Musk has sent out a personal, or, arguably, crude tweet about a progressive senator. He previously tweeted a sex insult at Sen. Ron Wyden, the chair of the Senate finance committee, who had criticized Musk for creating a Twitter poll asking if he should sell off 10% of his Tesla stock.

In response to a tweet from Sen. Bernie Sanders saying that the wealthy should "pay their fair share," Musk replied: "I keep forgetting that you're still alive."

Warren didn't take to Twitter to respond to Musk, but instead criticized the billionaire in a fundraising email sent out later that night. She called Musk "a poster child for how our rigged tax code lets billionaires pay hardly any taxes at all." She ran through some of his greatest hits, citing the over $100 billion that Musk added to his wealth during the pandemic.

"When someone makes it big in America — millionaire big, billionaire big, Person of the Year big — part of it has to include paying it forward so the next kid can get a chance, too," the email said.

She again called for a wealth tax.

Musk, unsurprisingly, took to Twitter to say just how much he'll pay in taxes. The expected total: over $11 billion.

As Insider's Jason Lalljee and Andy Kiersz reported, Musk could owe over $12 billion this year from taxes on his stock, taxes imposed by his previous home state of California, and taxes on net investment income.

The announcement by Musk made headlines — including at Insider — something that Warren took umbrage with. She wrote in a tweet that she has a plan to ensure it's not "breaking news when a billionaire actually pays any taxes."