Final answer:
The best evidence to support Addams' argument about politics in the late 1880s would be Newspaper editorials from influential publications, as they played a critical role in shaping public opinion and thus, political positions during that era.
Step-by-step explanation:
To best support Addams' argument about politics in the late 1880s, the most suitable piece of evidence would be Newspaper editorials from influential publications (A). Addams emphasizes the role that journalism played in shaping public opinion and political positions, as leaders had to engage with public opinion to pass laws and journalists became the mouthpieces of political positions. This era saw newspapers becoming increasingly influential in political debates, mirroring today's impact of social media on public opinion and policymaking.
The extensive presence of newspapers across America and their role in disseminating political content, whether they were owned by immigrants in various languages or subsidized by political parties, illustrates the pervasive influence of the press on politics. Not only did the newspapers publish editorials representing different viewpoints, but they also reprinted syndicated articles that spread widely, similar to viral content on modern platforms. The historical context, in which newspapers printed a variety of viewpoints including reader-submitted articles, supports the argument that a well-written editorial could have national reach and significant impact on public opinion and political landscapes of that time.