“Why does he look so angry?” one visitor to the National Portrait Gallery in Washington, D.C., asked our guide, as if that were a question with an answer. The docent had finally stopped before the black-and-white photograph of a looming, glaring President Trump that dominates the entrance to the final rooms of the “America’s Presidents” exhibit. We had managed not to talk about him for several minutes, swerving left toward the bright, kinetic John F. Kennedy painted by the abstract