Dobbs, the writer of the original books, was actually a Conservative Party big wig before becoming an author. A lot of people he dealt with informed the character.
Remember since FU is a whip his power comes from secrets. Skin color and place of origin don’t really play into that, just ability to fix problems and hold them over people later. That’s really the essence of the story, the guy who is the most powerful secret person in the country wanting to become publicly powerful.
intersting take on why the main character starts out as majority whip. You may be onto something. I think they minimize the Speaker, and the entire Senate for that matter - but I understand a series can only tolerate a limited number of characters.