There were times when Nazism was openly supported in the US, and when the KKK was mainstream, but there has never been a time when socialism was broadly acceptable. We had McCarthyism to "root out the Reds" but even the slightest attempt to push back against capitalism or the right meets with widespread backlash and oppression and violence by the state.

Even the so-called "leftist" party of the US - the Democrats - are pro police, pro imperialist, pro military industrial complex, anti-union and absolutely in bed with corporate interests. They may give lip service to some socially progressive ideologies but they will never do anything to threaten the status quo, and they can't even function without constantly moving to the right, whereas the right gets away with open sedition and treason without consequence.