Thanks to Laurie I learned that this blog suddenly started requiring commenters to log in. Catrina in Burbank told me the same thing about a month ago but at that time I just assumed it was a temporary bug. So, thanks to both of you.
At first I thought I needed to contact WordPress support to ask them about this. Then, like a ton of bricks, it hit me; check your settings dumbass! I did just that and found that the comments had somehow been set to “user must be registered and logged in to comment“.
I don’t know how that happened. I didn’t do it. I do not moderate comments here. Anyone is free comment here and say anything they like. What I found was that it was the non-Wordpress users that were required to be registered and signed in. The fix was a very complicated process. I had to uncheck a box.