Well no, but it is a long established part of the culture. The best objective way I could think of to indirectly measure it, based on the assumption that it is driven by tribal instincts to fight across polarized lines we can just look at congress.
See this animation as a reference: https://youtu.be/tEczkhfLwqM?si=JXKA6I8XDrlkvAcM
One can see the beginings of a divide noticably forming starting in early 1990, but then post 2001 the divide becomes very dramatic with almost no bipartisan agreement of any kind.
Both of these seem to coincide with wars, the gulf war of 1990's and the middle eastern wars (specifically afganastan and Iraq) from 911 onward.
So would seem the triggering event were our two major wars a decade apart.