A young sophomore Senator who, so far, has made a point to avoid having to dirty her hands with dealing outright with lobbyists against her conscience, is forced into an ugly situation by her party's Congressional leadership where she's forced to reach out and save her career by working across the aisle to undermine her party's leadership, as well as being forced to work for lobbyists.
The deeper idea behind this when I thought it up was concerning a young Democratic Congresswoman from Massachusetts who - while far from a Berniecrat - was nonetheless suspicious and distrustful of her party's leadership. Set during the incumbency of a Democratic President, party leadership begins leaning on this young Congresswoman for a vote she cast outside of party lines, and threatens her with pushing the DNC's PACs in her district to support a primary rival come the next election, to force her out. Desperation breeds a certain talent for politicking in the otherwise spotless Representative, and she starts to work to undermine her own party leadership by reaching out across the floor to sabotage the President's legacy bill, leaning on her boyfriend (the newly elected young leader of the Congressional Black Caucus), and working at last with lobbyists to try fight tooth and nail to keep her seat.
...For reasons that should be obvious, for the sake of making this story a political thriller in the vein of House of Cards, in this magical mystery parallel universe there is no Donald Trump in the White House

That would make for an interesting setting, sure, but not the one I'd ever envisioned when I had this idea xD