Examples could be democrats control over Biden's health messaging or republicans repeating the message that the democrats are stealing the elections or democrat's messaging about if their side loses it's the end of democracy or republicans messaging about immigration, crime etc. Generally engaging at a shallow level with the goal of influencing people's emotions.
I don't think this is a 40-2000 years phenomena. It's certainly become a lot worse since Trump ran for president the first time. I remember turning on TV in my hotel room during a visit to the US maybe 8 years ago and switching between CNN and Fox, each of these channels were basically about endless bashing of the opposite side. I wouldn't call the content anything other than brainwashing and propaganda. CNN didn't use to be like that. With social media since every user gets their own view we don't even know what the "hidden hand" is pushing. It's much worse and a lot more dangerous.