California Democrats have not even successfully passed their wealth tax ballot proposition, and they are already admitting it will fail to work as advertised. That is just one of the takeaways from a revealing social media exchange between wealth tax backer Rep. Ro Khanna (D-CA) and billionaire entrepreneur Mark Cuban.

Responding to a video posted by Khanna celebrating the California Democratic Party’s official endorsement of Proposition 40, a ballot initiative that would impose a one-time tax equal to 5% of billionaires’ net worth in the state, Cuban noted that many founders of successful technology startups become billionaires on paper long before they have anything approaching the tens of millions they would need to pay the wealth tax. Taxing that wealth would therefore force them to sell stock, borrow against it, or somehow extract cash from a growing company.