@justjennifer. Thanks again. I appreciate your time. The URL as you describe did not work when I tried embedding. The short-code provided by YouTube did and that is what I had used in all of the other posts without any problem until this week.
Maybe this is a situation of using whatever works, along with your instructions about the code being on a separate line and verifying that by using the text view.
I have noticed that when embedding YouTube videos into comments of other blogs with different themes, the URL and short-code work, while on other blogs/themes, only the short-code works.
Anyway, using the text view evidently worked for this situation. The video still appears (is embedded). I am grateful for your help.