When “Philip Guston Now” opened at the National Gallery of Art in Washington this spring, I could practically hear the collective sigh of relief on my Instagram feed. In 2020, shortly after the murder of George Floyd in Minneapolis and the nationwide protests that followed, the four museums organizing a retrospective of his work announced a four-year delay of the exhibition, citing the need to make sure they were contextualizing Guston’s paintings — which include a series of cartoonish images of Klansmen as bumbling Keystone Kops — with proper sensitivity.…