I’m more confused about where the term “Alt-Right” came from. Never heard it until the last presidential cycle and I follow politics pretty closely.
I’ll give a shot at answering your question. Often, the Left was called “Liberal”. For a growing segment of folks, there has been an attempt to grab back the mantle as a means of re-establishing the traditional political point of view of the Founders. The writers of the Constitution were considered liberals for their views of what constituted the best in human social and political arrangements. This is sometimes called “Classical Liberalism”. That’s one element. I lay out another element below.
So a question. With the Democratic Party moving further to the Left (realize this may be a controversial point, but believe it to be incontrovertible by the facts), how should that movement be described? How should those on the edges of that movement be called? “Leftist”, “Alt-Left”, or the more exacting label: socialist? As the Democrats consolidate around that pole of political thought, (again, I think this is incontrovertible with recent polling showing that outright socialism now has a majority positive view among Dems), how should we describe that leftward movement? One other “fact” in that this movement has accelerated in the last couple decades, Bill Clinton is no longer politically viable in Democratic Party - to the extent it’s true, he was part off the Conservative element of the Dem party formerly called "the Blue Dog Democrats - and now that is an extinct species. Hillary was made to basically renounce some of her husbands policies from the 90’s. One might argue that he slapped his name (i.e. Signed the bills) on Republican legislation, but he also then took credit for it - like welfare reform. That’s not possible in Democrat politics now.