Iyengar et al. (2012) shows affective polarization was substantial in the 1980s, establishing that partisan identity strength predates social media.

<iframe
  src="https://www.isonomia.app/embed/claim/796c57ddfe2c52461d49d2a72674bf94f9cce7c21413c3a5584b3649d2a70187"
  width="600"
  height="280"
  frameborder="0"
  style="border: 1px solid #e5e7eb; border-radius: 8px;"
  title="Isonomia Claim"
  loading="lazy"
></iframe>

Copy and paste into any website or forum that supports HTML.