Welcome to the world of dysfunctional Belief Communities.
"Americans ... values and basic beliefs are more polarized along partisan lines than at any point in the past 25 years." (Pew Research)
Pundits bemoan this polarization, and await a leader who'll cut the Gordian knot of gridlock politics to deliver us to a bi-partisan nirvana. The pundits will have a long wait.
America's current hyper-partisanship stems from a perfect storm of factors (described below). And it's created Belief Communities -- where people who want to believe patently untrue things (e.g., that President Obama was born in Kenya) are never challenged in their beliefs, and may even be encouraged in their fantasies.