Actually, I’m over 60.
And I’m not talking about “parties”, but various ideologically specified groups within parties. Actually, I suppose I’m really talking about those (and there are examples in both parties) who can’t really perceive the world in terms of more than “friends” who totally agree, and “enemies” who totally disagree. (See my response to Rogue Gay.)
I don’t really believe the preponderance of such people was present before sometime in Obama’s 2nd term, although my “evidence” is sparse and anecdotal.
Yes, there was tribalism, but IMO it wasn’t nearly universal, as it seems to be today.
It’s an interesting question, though. The 2003 rush to war against Iraq, and the number of “left-wing” MSM organs that joined it, was something of a surprise to me.