I have seen several examples of all sides working together for a common goal. One example would be the Lane County Poverty and Homelessness Board, composed of Eugene, Springfield, and Lane County leaders. 
A plane needs two wings to fly. A plane without a right wing or left wing will eventually crash. 
If your point is that the party in power needs to cooperate with those out of power, I sincerely doubt you really mean that. Trump and the Republicans own all three branches of government and will do everything they can to destroy the past work of Democrats. 

That is the law of the political jungle, and I would bet most who mock those who identify as liberal would agree with Trumpian logic.
Hugh Massengill, Eugene Oregon