What I mean by this, is that the bottom 50% of households don't pay any income taxes or very little. I calculated in a prior post that a family of four making $50,000 filing joint with two children pay roughly $1,500 in federal taxes using only the standard deduction. This would be less if they itemize. Now mind you, $50,000 is above the median income, but is a good proxy for "middle class" for most of the country. So the median family has an effective income tax rate of 3.5% How can you cut it more, Barrack? The top decile already pay the majority of income taxes.
So based on this, there is a limited amount of ways to cut taxes on the "middle class" based on this. Second, there are not enough "rich people" to soak with massive tax increases. Most of these people will just work less, thus depressing tax revenues. So the only way to the Democrat's tax plan to work is to define "rich" as low as possible - probably to the point where you're rich if you're employed.