Interesting review of Federal tax proposals

In general, the proposed numbers/percentages have problems – and this is interesting:

The U.S. tax system also stands out for its progressivity. In 2018, after the Trump tax cuts, the top 50% of all taxpayers paid 97% of all federal individual income taxes, while the bottom 50% paid the remaining 3%. However, state income taxes and payroll taxes are much less progressive.

Source: Biden Tax Hikes Have A Math Problem; The S&P 500 Might Too | Investor’s Business Daily

Interestingly, according to tax increase promoters, the top half does not “pay its fair share”. What would be fair share and how do you define “fair”?