People have been blaming Obama for divisions, because his Presidency and politics created resentment among white people.
You seem to want to blame, as it were, historical and social realities, because those things gave rise to the politics of identity.
Few, it seems, will just come out and say the direct truth: People are responsible for their own feelings, responses, and resentments. If there is division in our society due to white backlash against identity politics (and there certainly is), that division is being created by the resentful white people who can’t tolerate other identities having a political voice, and who don’t consider our democracy to be valuable enough to motivate them to educate themselves. Nor, obviously, do they consider marginalized voices to be valuable and equal enough to simply listen to them instead of freaking out and screaming for them to be silenced.