Nah, I think it's deeper than that. If the Catholic Church stopped believing in God and Jesus completely, would you still call them Christians/Catholics? At what point do we just throw our hands up in the air on a term?

Likewise with socialist/social democratic parties -- if they abandon all the tenets of socialism: worker control of capital, anti-capitalism, etc. but still keep the name... is it just that the content of the expression has changed? That seems a stretch.

However, I guess there's an argument to be made that "left wing" is so non-specific that it could do what you're saying. The phrase itself has its origins in the French Revolution with the Jacobins, etc. who were certainly not socialist. So I guess there's that.

But here's the thing. Many of the politicians called "left" in the United States don't even call themselves that. The right wing in the US calls almost everything "left wing". I stare in amazement at people who call Clinton or Biden "left wing"; they don't describe themselves that way, and actual socialists and left wingers don't support them (except grudgingly with their noises plugged when they have to vote).

But to the Tea Party and Trump types, they are "left wing." By which they just mean something pejorative