It’s why the Dems have worked so hard to stick to the good faith, even though the other party clearly hasn’t.

I’m not so sure the reason is quite so principled. I’m more inclined to believe the explanation in this video starting at about the 6:40 mark: the difficulty building a coalition in the Democratic Party (and especially the conflicting aims of Democratic voters and Democratic donors) causes the party to avoid policy and focus on process instead.