Sometime during the rise of BLM.
This. These were white voters who felt good electing a Black man in 2008 and 2012, they wanted to show their children that they were racially tolerant and colorblind. That they are not their grandparents or great-grandparents. A lot of people voted for Obama because they truly wanted a post-racial America. Truly, truly. They thought that would be the uniting force of the 2000s after the post-9/11 unity cratered around 2003-05.
Obama and BLM were created and BLM/woke people didn't do any favors saying "white man bad, white man evil should die out".
That is what turned them to Trump. A lot of them are not political either.