What's 'normal'? Pew Research data on political polarization in the U.S. (full report here http://www.people-press.org/interactives/political-polarization-1994-2017/).
A very dramatic drift toward the tails of the original distributions for both the Republicans and the Democrats, and, associated with this, an effective collapse in the numbers of the U.S. voters in the overlapping/shared position.
Removing the potential filter for political affiliation skewing the results:
Looking at pure preferences (excluding party identification), there has been a flattening (left-skewed) of public preferences spectrum. This also is consistent with growing polatization, but it is also consistent with increasing support by the voters for Extreme-Left and Left positions. The Center worldview has diminished substantially.
You can read my view on longer term trends and drivers for this dynamic here: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3033949.
