Michael Barone makes an interesting observation:
How will future historians explain this? From 2001 to 2014, majorities of Americans, including supermajorities of blacks and non-Hispanic whites, told Gallup pollsters that "race relations" were either very or somewhat good.
Then, after the election and reelection of the first American president of African descent, each case with majorities of the popular vote and electoral votes, perceptions suddenly plunged.
One possible explanation: a well-known observation (originally from de Tocqueville) is that revolutions tend not to start when conditions are absolutely bad, but when conditions are actually improving significantly but less rapidly than the middle class hopes for. O. was supposed to be this lightworker, this enormous change, but stuff was pretty much the same. Hence, despite much lower absolute levels of racism, misogyny, etc. etc. now compared with the past, frustration and anger.