Given how spineless Trump seems to be when confronted (judging from his reserved reactions to meeting with the Mexican president and Obama), it's entirely possible that without getting support from the Democrats in Congress he'd just fold on all of his big ideas and let the mainline GOP run the show while he acts as a big rubber stamp. If they can convince him to not give up on his plans that the GOP doesn't support, they could go a long way towards preventing them from getting too much shit done.