The useful thing about seeing 'Democrat' in a comment is that it is immediately obvious which way their bias leans.

What's wrong with "democratic" and why would it tell someone's political leanings? Isn't it just a different way to say "democratic"?

You must not be from around here.

https://en.m.wikipedia.org/wiki/Democrat_Party_(epithet)

In this case I don't see why it needs to be an adjective.

By analogy, you'll more often hear "Texas senator Mr Bean" (using the singular noun) vs "Texan senator Mr Bean" (using the adjective).

In any case, it's not something anyone should get worked up over.

Let's ask Google.

  "democratic senators"
  > About 969,000 results (0.52 seconds)

  "democrat senators"
  > About 92,800 results (0.42 seconds)

Bonus:

  "democratic senators" site:breitbart.com
  > About 1,010 results (0.32 seconds)

  "democrat senators" site:breitbart.com
  > About 2,300 results (0.27 seconds)

Conclusion: "democratic" is significantly more common outside of right-wing propaganda.

I'm well aware... but in this particular sentence he or she is talking about specific Democrat, not the Democratic Party, and as such, seems grammatical.