It's funny, because I watched it play out in real time on Reddit.

It all changed with the Tea Party. Not at first - a fact that the statists on both sides of the aisle want to bury is that the first couple of Tea Party protests were genuinely libertarian, and were in fact against the Bush administration.

But when Obama was elected, the Republicans moved to co-opt the Tea Party, and succeeded, and both they and the statists on the left were then more than happy to pretend that it was always a Republican thing, since as much as they might differ on the details, they both agree that the idea of being free of government entirely cannot be allowed to prosper.

And almost immediately, r/libertarian went to complete shit, as it was taken over by overt authoritarians who just want to eliminate all of the bits of the government they don't like - like gun laws and public assistance of any form - so the rest of the government can then focus entirely on punishing people for being too liberal or too brown or too smart, and they themselves can be free to just shoot anyone they want.

It took me a while to figure out that that change wasn't limited to just Reddit - that libertarianism as a whole had been co-opted by those violently authoritarian shitstains.

And it's certainly not a coincidence that the net result of that is that there's no longer an umbrella term in the US for people who just want people to be more free, and "libertarianism" has become just another variety of authoritarianism.