I think enthusiasm can help either side. Trump’s favorability ratings are higher than in 2020. I do think that we may see an end to Harris’ honeymoon period and a drop in enthusiasm for her. However, since Trump would be expected to get at least a minimal bump from the convention and assassination attempt, any shift at all toward Harris is probably underestimated.
I do see opportunities to keep the enthusiasm going with the official nomination, the VP selection and the convention as well as possible debates and possible Trump sentencing.