“Cancels” is the wrong verb again. ABC can cancel it, Trump can only decide not to show. ABC and Kamala can go ahead and have a debate with the audience or even put a cardboard cut out in his place and play random quotes he’s made and let Kamala disagree with them. ABC would get views and advertising revenue.
The right neutral verb phrase there is “backs out of”. The one I would pick is “shirks” or “fears”