"See , we told you the other side was crazy"
911 truthers & marxists have always existed, however its only when the "mainstream" of the other side chose to hand the fringe a megaphone, that they came to the fore.
This was not done for debate or charity. It was to score cheap political points in the age of clickbait. Extra Bonus: they got to extrapolate the extreme over 50% of the US population, and by consequence, to expand their potential eyeball audience
And the reason it's blowing up now is because the media monopoly is over. Back when "the media" was ABC, CBS, NBC, AP, UPI, and then-centrist New York Times and Washington Post, nobody was giving the crazies the microphone, on either side. But when Fox and talk radio came on the right, and CNN on the left (and many of the former-center media moved left), then there were people with a slant, and therefore with a motivation to make the other side look silly.
But these people (on both sides) need to reconsider what they're doing. They're making the other side look silly to the mainstream, but they're also helping the fringe of the other side recruit. That may not be a very wise policy...
Between radicalised parties it looks like that everywhere. When people have only two choices, by necessity each choice contains radicalised fringe elements. For some reason societal factors in the US give these elements a huge presence, which I don't really understand.