While I cannot disconfirm the former (though there have certainly been some high profile cases with fishy circumstances- such as JFK), what about the Russiagate nonsense with Trump? I might hate him but the manchurian candidate theory was transparently bs from the very beginning, even before the investigation that proved it. He's certainly not the first politican that this line was used on and will probably not be the last. It seems to be a bipartisan thing to simultaneously shift focus of the public from national level corruption in favour of a foreign bogeyman and simultaneously slander opponents.
In a so called representative democracy, you do not need to outright murder or imprison your opponents to enforce control, you simply either have to relegate them to irrelevance through skewed or absent corporate media coverage or buy them out. See Bernie Sanders, Tulsi Gabbard, Andrew Yang, early Nancy Peloski, AOC, etc.
The tactics might differ from a transparently autocratic regime but the intentions are the same, and the end result is not really as different as liberals like to paint it. For all the unpopular politicians that are allowed to continue, there is police violence, surveillance, torture, imprisonment, and outright assasinations of prominent figures in activist groups. Then there is what they get up to outside the confines of US citizenship and borders.
Look at the state of Bolivia, Columbia, most of Central and Southern America actually. They have death squads from paramilitary groups backed by US multinational companies for the sole purpose of brutally putting down any attempts at collective bargaining or real democracy. Just because it's not visible in your backyard doesn't mean your country is not responsible for that mess.