It is a general rule of American, known to politicians across the land, that once huge, society-reorganizing measures, are passed, rarely if ever do they go away. Many come to depend - or to falsely believe they depend - on them, and will lash out vehemently at attempts to repeal, becoming valuable voters to those who would expand or protect these policies.
Seen through this lens, one understands why the Democrats want to ram their reforms soon no matter what the opposition.