From Pew Research Center:

Over the past month, the increase in the percentage saying the campaign is interesting has come entirely among Republicans and independents. In the new survey, conducted before Monday’s debate, 73% of Republicans say the campaign is interesting, up 23 points since early September and by far the highest percentage of the year. More independents also view the campaign as interesting (56% today, 45% in September). The percentage of Democrats who say the campaign is interesting, which jumped 19 points between June and September, is unchanged since then (66%).