It's been that way since Newt's contract on America & probably before.
Definitely before. People like Nixon (and even other horrible people) were pushing that type of garbage (sadly, he was even getting Eisenhower to sign off on stuff like that too) decades before then. Its just that we've often had other things to collectively be concerned about (post WWII world, nuclear war, Cold War, various actual wars that grew out of that, and then gas crisis and economic issues). The thing is, if you look at things objectively, you see all of that actually leads back to conservatives/Republicans and the wealthy that were manipulating everything.
I know people want to believe things are worse in regards to the rhetoric and other stuff, but they really aren't (it kinda ebbs and flows, but its been there pretty consistently, which periods where it reaches a fervor). Its just that given history, its easier to see how toxic that stuff was and is, and how it actively works against human interest. This is the same mentality that gave us McCarthy's bullshit, the anti-Civil Rights mentality, the "race wars are coming!" idiocy, the "its the Mexicans/Muslims/Soviets!" scaremongering, among various others that I'm sure you can probably think of or see.
The reason things seem different is that, via various means (including outright lies) they used to get some on both sides of political ideology on board, but now even Centrists see it for the bullshit it is (but its still hard to get people to actually put the brakes on it, as its easy to buy into the "well if you don't fall in line and support it, it will just increase its chance of failure, hurting us/America more, even if its completely wrong, its better that we unite to "win" than since its gonna happen anyway). That's not to say it can't still work, like with the 2016 election, but look what it took to enable that. It took one of, if not the most, widespread disinformation campaign in human history (well at least per relatively specific instance, not the sustained ones that; which even then you could argue its a continuation of several of the long-sustained ones that coalesced into a singular goal).
In a lot of ways, its a testament to how much smarter people are compared to even 50 years ago. And that, even though it can be used for nefarious intent, the technology has actually worked some, where people are more informed. People bemoan how many willfully stupid people there are, but they were always there, but now they have to do that in the face of a barrage of actual information and knowledge, and it is working. Yes, for many they're in that transition phase where they're so locked in mentally, that contradictory information makes them more stubborn and resolute.
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