There's absolutely zero requirement for posts to be news in the sidebar, let alone a definition of what they consider "valid" news sources. In fact, everything there directly supports posts like this.
First line of the sidebar?
Welcome to the discussion of US Politics!
Yup, certainly fits. Next to the rules.
Post only links to articles, Title must fairly describe link contents. If your title differs from the site’s, it should only be to add context or be more descriptive. Do not post entire articles in the body or in the comments.
Links must be to the original source, not an aggregator like Google Amp, MSN, or Yahoo.
"Article" is not a word solely for newsprint or journalism. If that's their intent, they need to say so and explicitly define what qualifies as "news" (problematic on its own, but for another discussion).
Articles must be relevant to politics. Links must be to quality and original content. Articles should be worth reading. Clickbait, stub articles, and rehosted or stolen content are not allowed. Check your source for Reliability and Bias here.
Aside from the nebulous and subjective requirement for "quality", nothing here specifies "news only" either or disqualifies the OP post.
The rest of the rules just cover behavior and general tos. So, if anything, an original article discussing US politics in the "discuss US politics" community should be welcomed by any mod acting in good faith.