Dems need to keep all their congressmen and senators in line. Can they continue to do this as they go further left?

Three votes in the house and one vote in the senate would keep them from continuing to bulldoze spending through congress.  Some of those house members and senators are from purple districts/states, or even red districts/states that experienced an anti-trump backlash in the last election.  It is about a 90% chance that the house and perhaps the senate will change hands at the midterms, but can the dems hold their members together until then?