The answer is the Middle Class.
The lower class doesn't pay taxes, they get stipends.
The upper class has the Internal Revenue Code to provide thousands of ways to reduce or even eliminate paying taxes.
The Middle Class. The 1986 Tax Reform Act took away the useful deductions from this class.
The Middle Class consists of blue and white collar workers that work most of the year just to pay taxes.
The middle class is not represented by either political party.
The democrats focus on the lower class, and the republicans focus on business and the wealthy. Cliche, but still true even today.
The middle class has shrunk, and continues to shrink since 2008. Many have fallen into the lower class, and some at the upper upper middle have made it to the upper class.
The democrats under either Hillary or Bernie will continue to grow the lower class, as this is their base voting class.