This is an Echinocereus triglochidiatus in a 5 gallon pot, growing outside for several years. At the end of the summer I noticed that there was a really rotten stem. The rot was of the very wet type. I removed as much of the rot as I could and sealed the wound with a lot of super glue. This is enough rot, I think, to eventually kill the plant. Spring 2020 will tell me if I did it any good.