If we were to look at basic leftist theory they always regard liberals as non left. The argument is that liberals just protect the liberties of the priviledged class, typically the wealth owning class. They treat the workers like wage slaves, throwing them a bone to keep them quiet, but when historically being forced to choose between having the workers attain same level of liberties, the liberals always chose to surpress that, break unions or even multiple times directly allow fascist overtake.

you are right that in us this is presented as opposition, but any serious leftist will categorically deny that as absurd. One good indicator is for example how the genocide in gaza is bipartizan or even the war in iran. They protect same interests. They do not serve the voter.