Current cross-platform social media analyses primarily focus on the textual features of posts, often lacking multimodal analysis due to past technical limitations. This study addresses this gap by examining how U.S. legislators in the 118th Congress strategically use social media platforms to adapt their public personas by emphasizing different topics and stances. Leveraging the Large Multimodal Models (LMMs) for fine-grained text and image analysis, we examine 540 legislators personal website and social media, including Facebook, X (Twitter), TikTok. We find that legislators tailor their topics and stances to project distinct public personas on different platforms. Democrats tend to prioritize TikTok, which has a younger user base, while Republicans are more likely to express stronger stances on established platforms such as Facebook and X (Twitter), which offer broader audience reach. Topic analysis reveals alignment with constituents' key concerns, while stances and polarization vary by platform and topic. Large-scale image analysis shows Republicans employing more formal visuals to project authority, whereas Democrats favor campaign-oriented imagery. These findings highlight the potential interplay between platform features, audience demographics, and partisan goals in shaping political communication. By providing insights into multimodal strategies, this study contributes to understanding the role of social media in modern political discourse and communications.

翻译：当前的跨平台社交媒体分析主要关注帖子的文本特征，由于过去的技术限制，往往缺乏多模态分析。本研究通过考察美国第118届国会议员如何策略性地利用社交媒体平台，通过强调不同议题和立场来调整其公共形象，从而填补了这一空白。利用大型多模态模型（LMMs）进行细粒度的文本和图像分析，我们研究了540名立法者的个人网站及社交媒体（包括Facebook、X（Twitter）、TikTok）。研究发现，立法者会调整其议题和立场，以在不同平台上展现不同的公共形象。民主党人倾向于优先使用用户群体更年轻的TikTok，而共和党人则更可能在Facebook和X（Twitter）等受众更广的成熟平台上表达更强烈的立场。议题分析显示，其内容与选民的核心关切保持一致，而立场和极化程度则因平台和议题而异。大规模图像分析表明，共和党人更多使用正式视觉元素以彰显权威，而民主党人则偏爱以竞选为导向的图片。这些发现凸显了平台特性、受众人口统计特征和党派目标之间在塑造政治传播过程中潜在的相互作用。通过提供对多模态策略的深入见解，本研究有助于理解社交媒体在现代政治话语和传播中的作用。