Which statement is true about partisan behavior in the 19th and 20th century U.S. Congress?

Partisan behavior in the U.S. Congress during the 19th and 20th centuries was characterized by a significant degree of partisanship. This period saw the emergence of organized political parties that played a pivotal role in shaping legislative priorities and influencing votes. The polarization between the major parties, particularly as issues such as civil rights, economic policies, and foreign affairs evolved, resulted in lawmakers often aligning closely with their party's platform.

Throughout this time, the influence of parties on Congress grew stronger, with party leaders exerting control over committee assignments and legislative agendas. Members of Congress often voted along party lines, reinforcing the idea that partisanship was a defining feature of legislative behavior. The development of strong party identities among both Democrats and Republicans contributed to a highly partisan atmosphere, where party loyalty was paramount and significant divisions emerged over key policy issues.

In contrast, the other options either downplay the role of partisan behavior or imply less definable partisan influence, which does not align with the historical context of these decades in Congress. Thus, the assertion that partisan behavior was highly partisan accurately reflects the reality of congressional dynamics during this era.