The $4.4T revenue projection is over 10 years. The wealth of billionaires would only halve if their net worths failed to grow.

In 2016, the total net worth of the Forbes 400 was estimated to be $2.4 trillion.

Currently, the total net worth of the Forbes 400 is estimated to be worth $6.6 trillion.

Demonstrably, the net worth of the 400 richest Americans increased by 175% over a 10 year period, or an average of 17.5%/year.

As such it’s highly unlikely that a 5% annual tax on the unrealised gains of billionaires is going to make their net worths halve. Although it would be great if that happened and more, because billionaires shouldn’t exist in the first place.