Elizabeth Bruenig has written about the distinction between “liberals” and “the left.” She proposes that everyone in the broad tent of what she calls “non-Republicanism” is actually a liberal, in the following sense:

The second sense in which almost every non-Republican is a liberal is that they all agree with the tenets of liberalism as a philosophy: that is, the worldview that champions radical, rational free inquiry; egalitarianism; individualism; subjective rights; and freedom as primary political ends. (Republicans are, for the most part, liberals in this sense too; libertarians even more so.)

This is an easy statement for me to agree with — but I also think it brushes past some political distinctions that are important.