Differences between parties are often small. Democrats want to spend more and don't want to raise taxes, except on high earners. Republicans want to reduce taxes but don't want to spend less.
--Robert J. Samuelson
Samuelson, no relation to the economist, is a contributing editor to both Newsweek and the Washington Post.
Politics are a tribal matter. We are born into our politics. Once we've bought into the party line, we tend to reside in homogenous neighborhoods where residents support our party. We tend to adapt our ideas to the party, ignore ideas that differ from our party, paying little attention to the ideas of the opposition party. As Samuelson notes, the other side cannot be merely mistaken. Instead, differences are morally distinct. It must be evil, selfish, unpatriotic, immoral or just stupid. Polarization deepens and compromise becomes more difficult. That, also, makes it more difficult for us to talk about political or governmental issues.