The executive branch has a lot less power than people think it does. Aside from the executive orders on "how" to implement laws that congress passes and the curtailments to power by the Supreme Court, they don't have much control over the purse strings. If congress doesn't like the "how" they either update the law or have the SCOTUS to make a ruling that says they don't have that power in the first place.
A president can say to congress "I'd like you to pass a bill that..." and they can change some things for federal workers - but for states, they've got very little regulatory power outside of what has been granted to them through the various departments (e.g. Department of Education).
2016 had a 52/46/2 senate composition with a republican majority. The house was 241 to 194 with a republican majority.
My crystal ball for a hypothetical president Sanders shows a president who would have been able to do very little except for some executive orders which would get overridden by congress. The house would have been very unlikely to give him the budget to fulfill his promises and ideals while blaming him and every executive branch agency for every failing and catastrophe that occurred in 2020.