The DNC does have the ability to make, e.g., expanding the SCOTUS a plank in its platform. While it can’t force its candidates to support every policy plank, it does have substantial ability to reward good behaviour and punish bad behaviour.
The problem is that the current party leadership is too risk-averse and complacent and mired in the past to either take a firm stand on actual systemic reform (e.g. ending the filibuster) or on imposing discipline on members who reject it.
Compare to the other duopoly party, which is explicitly committed to preserving and enhancing the most broken elements of the system and which whips its members hard to stay in line.
The Years quote applies to both party leaderships: “The best lack all conviction, while the worst are full of passionate intensity.” The poem the line comes from is very descriptive of the current American political scene too.
