Republican politicians and right-wing media can’t attack Biden because he is popular. Their supporters don’t hate him because he is a white man unlike Barack Obama and Hillary Clinton. They don’t attack his policies because they are popular, too.
Instead, they stoke the culture wars – Dr. Seuss, Mr. Potato Head, and now CRT. CRT is not taught in K-12 schools. It’s an undergraduate/graduate school level subject. However, talking about it inflames the white nationalist Republican base.