You're asking the wrong question. Its not has prejudice and racism increased under Trump as the article points out. The question is why has the incidences of overt racist violence and actions increased so steeply and significantly under this president?

The racists, when they took the initial survey are stll racist. The difference then becomes, "What has changed to embolden these racist to overtly act out now, when they didn't before?"

This where the correlation does imply causation. The president sets the moral, ethical, and acts as a role model for the country. Its part of the job, like it or not. The country looks to the Office of the Presidency for leadership in these areas.

This president, due to his own racism and misogyny has given implicit and explicit permission to the racists in this country to act out. His condemnations have been teleprompter scripted and always delivered in an unbelivable lukewarm presentation. He is easy to read when he belives in something, he is enthusiastic and animated. When he doesn't, but is forced to by political necessity, he is blase' and flat. His condemnations have all bern blase and flat. Add to this the dog whistle comments he throws into his animated oresentations and you have a direct relationship in the rise in racial acts and violence and the presidents words and actions .

So recap, like it says in the article, the number of persons who are racist hasnt necessarily increased. But thevnumber of overt violence racist actions have. That is a direct correlation between this increase and this president. This is one place where correlation is directly linked to causation.