Trump did not condemn Roseanne Barr’s racists tweets. Instead, he used it as an opportunity to make the issue about himself and demand apologies.
Trump is a racist as he has shown repeatedly so it’s not surprising he didn’t disagree with Barr’s tweets. He has no interest in uniting the country. He only cares about his base.
Not all Trump supporters are bigots but I think a lot of them are. He didn’t attack Barr’s remarks so he wouldn’t offend them. I don’t blame Trump for Barr’s tweets but he has created an environment where bigots are more open because of his encouragement.