Presidential debates are critical platforms for political discourse, yet existing research lacks datasets tailored for analyzing real-time professional commentary. To address this, we introduce the Dataset on Real-time Commentary in U.S. Presidential debates (DR-CUP), which aligns U.S. presidential debate transcripts (2016–2024) with professional commentary and annotations. DR-CUP supports research on commentary understanding, planning, and generation, offering insights into expert analysis and its role in contextualizing complex political discourse. In pilot studies, we evaluated state-of-the-art large language models (LLMs), revealing notable performance differences in understanding expert commentary and planning for generating professional commentary. DR-CUP is the first dataset to incorporate real-time cross-document alignment for debate data, providing a comprehensive resource for advancing research in political communication and computational social science.