I watched a bunch of youtube videos, then took out the circulation pump and took it apart. Nothing obviously wrong or stuck. I cleaned it and put it back together. And now the dishwasher seems to be running!! AMAZING.
Of course, I had to loosen a couple of hose clamps and I broke at least one stupid little plastic bit while taking the pump off. So probably won't last long. But I appreciate at least one more load of dishes my machine will do for me!