It's really pretty simple.  Bush Jr. took us far in the wrong direction, he and the R's had very little of the countries support at the end.  So Obama looked like the opposite of Bush and people went that way.  The only problem is the far left is not a great place to be either.  People had 8 years to forget about Bush and we are headed back to the far right.  Maybe someday we'll find middle ground.  Groups like the Tea Party, Occupy ?, Black lives matter are a big part of the problem.