The most leftist primary candidate with any kind of shot was pretty centrist by, say, NATO standards. We've evidently convinced ourselves that it's a short hop from government involvement in medical coverage [or insert barely progressive Democratic plank of choice] to communist hell.
It isn't really "the commies" that is at issue here. It is the initial form of Liberalism as practiced in the 1780's. It established one hell of a stronghold in the United States of America c/o the founding fathers.
And that form of Liberalism expressed "power to the people" by way devolving power
away from the government and to
the individual rather than
the collective. So anytime you start talking about government programs that remove or displace
individual rights in favor of anything else, you see a massive cultural backlash get unleashed against it.
Sure, whatever is being peddled may benefit the individual in question if they agree to cede some of their individual rights, but they're not going to surrender them casually all the same. Sometimes even more so in that case, as they know that if they're benefiting, someone else is probably losing, c/o the magic of government, and a LOT of people in the U.S. will reject such an exchange as a matter of principle--as they wouldn't want to be the person on the (government enforced) "losing side."
Edit to add: Or to frame it another way...
"Liberalism" in the United States remained essentially "frozen" in the late 18th Century because we achieved a stable working, liberal representative republic that has worked reasonably well without much in the way of major problems up through the 20th Century. It worked, people were happy with it, so it remained and remains as the defacto status quo.
Meanwhile, "Liberalism" as practiced in the rest of the world, continued to morph and adapt to the various changes that came with Industrialization, the Steam Engine, telecommunications, etc. That everyone else, bar the British Empire, failed to remain stable throughout all of that just enabled the concepts and practices to continue "to evolve."
They also likewise never had the strong impetus towards Individualism like happened in the United States. The British Empire and now, the members of the British Commonwealth, also never developed "major problems" with the idea of a powerful central government. While the idea of a Strong Central Government still causes people to freak out in the United States thanks to rhetoric from the Revolutionary War against the Crown and Parliament of Great Britain.
