Following news Wednesday that Sen. Bernie Sanders underwent heart procedure to treat an artery blockage, Sanders speechwriter David Sirota demanded that billionaire financier Steve Schwarzman apologize for his comment Tuesday evening that "maybe Bernie Sanders shouldn't exist."

"Maybe Steve Schwarzman should apologize for making such a disgusting comment," Sirota tweeted Wednesday.

"I'm not going anywhere. But billionaires can be damn sure they'll pay their fair share when I am president."

—Sen. Bernie Sanders

Schwarzman's remark came during an event promoting his book at the New York Public Library Tuesday night. The financier and adviser to President Donald Trump was asked to respond to Sanders's recent comment that billionaires, as a class, should not exist.

"I don't think that billionaires should exist," Sanders, a 2020 Democratic presidential candidate, told the New York Times last month in an interview on his wealth tax plan. "This proposal does not eliminate billionaires, but it eliminates a lot of the wealth that billionaires have, and I think that's exactly what we should be doing."

Sanders hit back at Schwarzman on Twitter Tuesday after the billionaire's comments surfaced online.

"I'm not going anywhere," tweeted Sanders. "But billionaires can be damn sure they'll pay their fair share when I am president."

I’m not going anywhere. But billionaires can be damn sure they’ll pay their fair share when I am president. https://t.co/oV4bj9gm3T — Bernie Sanders (@BernieSanders) October 2, 2019

Warren Gunnels, a senior adviser to Sanders, estimated Schwarzman would pay over a billion dollars more in taxes under the Vermont senator's wealth tax proposal.

"Schwarzman is worth $17 billion," Gunnels tweeted. "He would pay over $1.1 billion more in taxes under Bernie's plan to tax the extreme wealth of the top 0.1 percent. Schwarzman also compared Obama to Hitler when he tried to close the carried interest loophole. Disgusting."