What was James Shields known for in U.S. politics?

James Shields is primarily known in U.S. politics for being the only Senator to serve from three different states—Illinois, Minnesota, and Missouri. This remarkable feat is not only unusual but also highlights his unique political career and adaptability across different political landscapes.

Shields began his Senate career representing Illinois as a Democrat, then moved to Minnesota, where he continued to influence the political scene. Finally, he served as a senator from Missouri, making him a distinctive figure in the history of the Senate with his representation spanning across multiple states. This aspect of his career underscores his political maneuvering and ability to maintain relevance in various regions of the country during his time in office, which was less common in the era in which he served.

In contrast, the other options do not accurately represent his legacy: he was not the youngest senator, nor did he govern multiple states in a significant way, and while he was involved in legislative activities, he is not primarily recognized for writing major legislation. Thus, the unique aspect of his service from three different states solidifies his place in U.S. political history.