Two current New York museum shows, one about events between Mexico and France in the mid-19th century, the other about Germany in the early 20th century, provide uncanny political and esthetic windows onto our current moment. Each exhibition comes on like a fever dream. The first shows a single artist, Edouard Manet, striding into a future that bumps directly against the present. The other captures a group of German artists desperately reaching into the stylistic past to picture humanity in a state of utter depravity and pain. Each exhibition treats history as a kind of tragedy -- a downward spiral that many saw unwinding but could not circumvent.