There were actually two prison reform bills proposed by congress. Both having the support of the majority.
This bill, the one Trump is supporting, is the least expansive and progressive of the two initial proposals.
Ironically, the better bill that is being shutdown is also bi partisan, but Co sonspored by chuck Grassley and Durbin.
The only reason it hasn't been signed into law yet is Trump. He initially said he'd vote against the Grassley Durbin law saying it went too far and favored the one of his son in law.
During the interim fukkery the house and senate actually carved out a compromise that has a veto proof majority. Trump's just taking credit for something he ultimately letting stall
From may: