So long as there have been communists there's been people accusing everyone to their left of being communists.

Wikipedia describes the first Red Scare as happening in 1917, after the Soviet revolution and WWI. But you can also look at labor movements before that. For example, in the Haymarket Affair in 1886, someone in a crowd threw a bomb at a police officer during a protest, which has been speculated to have been a plant. The point was to smear the whole labor movement as anarchists and communists, as violent radicals, even though many of them were not.

But we can go even further back, in 1848, the opening lines of the Communist Manifesto are:

A spectre is haunting Europe — the spectre of communism. All the powers of old Europe have entered into a holy alliance to exorcise this spectre: Pope and Tsar, Metternich and Guizot, French Radicals and German police-spies.

Where is the party in opposition that has not been decried as communistic by its opponents in power? Where is the opposition that has not hurled back the branding reproach of communism, against the more advanced opposition parties, as well as against its reactionary adversaries?

Karl Marx himself is already talking about how every center-left opposition party is accused of being communist, and about how those same center-left parties will hurl the same accusations at parties to their left, and even against parties to their right ("reactionary adversaries").

Yes, the Nazis branded progressives as communists, and the Nazis did come up with things like "Cultural Marxism," but they were hardly the first ones in history to do it.