“Ms. Viso’s history with “Scaffold” goes back years. She recalled first seeing it on exhibition in Europe and proposed the work to the Walker; the board signed off on the $450,000 purchase in 2014, according to minutes from the Walker board’s acquisition committee. Walker curators were aware that other work by Mr. Durant dealt with the Dakota war, and the museum has acknowledged that it should have engaged in a meaningful way with Native American leaders before mounting “Scaffold.”