Post preview running lines of a poem together

Are you actually hitting “Enter” after each line, where you want the line break? If you’re not, WordPress isn’t putting in the <br/> code to tell the browser to break that line of text.

You can always switch over to the text editor and manually add the <br/> yourself.

Hope that helps.

The line breaks are there fine in the actual article.
Compare what appears in the summary for “Haiku Lament” at https://www.ericbeversluis.com with what appears at https://www.ericbeversluis.com/haiku-lament/.