You are way off if what you are saying is that Obama caused white racist activism and the Alt Right and White Supremacist movements. Unless your idea is that Obama or any black speaking out against racism and hatred toward blacks leads to white racism. As to Trump, things he said attracted the very vocal support of many of the racist Alt Right, White Nationalist, and White Supremacist groups. They heard a message from him that they thought meant that he supported them. They feel that Trump has made it “politically correct” to say what was “not politically correct” before— to speak and advocate racism and hatred of blacks (and for many of these groups, hatred of non-Christians— including Jews and Muslims— and non-whites).