Probably getting rid of Citizen's United, taxing the wealthy correctly, getting rid of the electoral college, reworking the makeup of the Supreme Court, and ranked choice voting would do most of it. All hard but doable.

Theoretically we could end the electoral college next year. There's a thing called the National Popular Vote Interstate Compact. We now have trifectas in enough states for it to go in effect, should a few more states join. We also have Congress too (needed because they'll have to approve it). It's unlikely the federal government can force the states to do ranked choice voting without a Constitutional amendment. But we could implement it on a state by state basis. The Supreme Court could be reshaped by the next President and a willing Congress - the needed precedent is already there in the circuit courts. Citizen's United is trickiest. The straightforward approach requires either a Constitutional amendment or the Supreme Court to overturn itself. But it's possible there's some tricky alternate paths to accomplish the goal. One of them is convincing enough states to ban corporate spending on political speech. Since corporations are a state creation, they alone have that sort of power. Problem is even one non cooperating state could possibly ruin that. But there might be other ways too.