I have lost the ability to trash mail messages in the Mail App

I have an iMac, OS 10.13.1, and recently lost use of the trash can in Mail. The trash can is not dark in appearance. I now have to drag the subject to the left until a red delete button appears and click that so the mail appears in trash. Before this latest instance I could hit the DELETE 'key on my keyboard and trash 1 or a group (select all) emails.