Mark Cuban, the billionaire entrepreneur and former owner of the Dallas Mavericks, had an intense exchange on CNBC’s Squawk Box this Thursday after host Rebecca Quick challenged him on Vice President Kamala Harris’ controversial tax proposal. Harris has endorsed a plan to tax unrealized investment gains, targeting some of the wealthiest Americans. The debate left Cuban visibly flustered, leading to a moment where he repeated the word “no” sixteen times in a row.

The heated exchange occurred after Quick suggested that Harris was telling voters “what they want to hear,” implying a disconnect between her public messaging and what Cuban had been told privately. However, Cuban’s primary objection to the plan is its potential impact on the stock market. He argued that taxing unrealized gains—investment profits that exist on paper but haven’t yet been sold—would have catastrophic consequences for the economy.

“If you tax unrealized gains, you’re going to kill the stock market,” Cuban said. “It’s going to be the ultimate employment plan for private equity.” The billionaire also spoke from personal experience, recalling the early days of the dot-com boom when his wealth was tied up in stock, but he had little actual cash. Under Harris’ proposed plan, Cuban said he would have been forced to borrow money just to pay his tax bill on unrealized gains, which could have crippled his ability to run his company.

The Democrat-led plan has faced significant criticism from economic experts, private investors, and business leaders. Many argue that the logistics of calculating unrealized gains and taxing them would be highly complex and could lead to unintended consequences, such as a mass sell-off in the stock market. Additionally, the proposal has not gained broad support in Congress, making its path to becoming law uncertain.

Quick pressed Cuban on the Harris campaign’s inconsistency. Cuban then claimed that Harris’ team privately acknowledged the potential problems with taxing unrealized gains but insisted that the details needed to be worked out. Quick countered, saying, “But the election is in 60 days. You’ve got to get the details right now.”

“No, no, no, no, no, no, no, no, no, no, no, no, no,” Cuban said. He then attempted to downplay the urgency, claiming that even if it took until the day before the election to finalize, the important thing was getting the policy correct. Quick was not convinced, pointing out that voters need clarity on such significant policy proposals before heading to the polls.

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Harris’ support for taxing unrealized gains aligns with Joe Biden’s proposal for a 25% minimum tax on the wealthiest Americans. Under this plan, individuals with a net worth exceeding $100 million would have to report their unrealized gains annually. These unrealized gains are the difference between the asset’s current market value and the original purchase price, even if the asset has not been sold.

The proposal is part of the effort by the Biden administration to ensure that billionaires and ultra-wealthy Americans pay their “fair share” in taxes. It’s often referred to as the “billionaire minimum tax,” targeting individuals who, according to advocates of the plan, benefit disproportionately from the current tax structure.

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