Commentary To help fund his over-the-top spending proposal of $5.8 trillion in post-COVID Fiscal Year 2023, President Joe Biden has called for a brand-new tax on wealth in addition to the current tax on income. He would tax assets that have appreciated since they were purchased. This sounds like a capital gains tax, but it has an entirely new wrinkle: The tax would be levied before the owner actually sells the asset and realizes a gain. It would be a tax on a paper gain—a phantom gain, not a real one. Biden’s political allies have come forth trumpeting the alleged virtues of such a tax. As typified in a Wall Street Journal opinion piece by Jason Furman, a Harvard economics professor who served as chairman of the White House Council of Economic Advisers during President Barack Obama’s second term, progressives claim that such a tax would be “fair.” Is that …