From the White House:
"The federal government is projected to spend $4.091 trillion next year, with roughly two-thirds of that going mostly toward Social Security, Medicare, Medicaid, poverty assistance and interest payments on the government debt. This spending is expected to be left untouched in the budget proposal next week."
You can't reduce the size, cost and impact of the federal government without reforming entitlements -- which Trump and liberals flatly reject.
Only about 16% of the budget is non-defense discretionary spending - stuff like the Department of Education and EPA.
Trump's "historic cut" is taking a small slice of that 16% and transferring it to other programs. Those programs should be eliminated, not cut, and those funds returned to taxpayers, not spent elsewhere.
The federal budget pie will continue to grow larger under Trump. The only difference is non-defense discretionary will account for less than 16% as he expands spending in other areas.
In other words, Trump isn't doing squat to reduce the size of the government.