Of course race relations were worse post Obama. They are drug dealers and rapists.
All presidents are attacked at every turn. The high road is optional. The other presidents mostly took it, but Trump figured he would make political hay with his Crazy Nancy, Cryin' Chuck and so on and so forth. Virtually every day he communicated his disgust of over half of the country or their duly elected representatives. In the end, he threw a good portion of his own party under the bus as well. He successfully sowed division, but didn't understand the split. Not really a mistake as he wouldn't have had his success without that behavior. That defines him.