This plot development doesn't work for me. For five years, Beckett's been defined as someone who cares passionately about speaking for the victims of crime and bringing their killers to justice. She's already doing the job she wants to do more than anything. So this idea that working for the federal government is her greatest ambition in life comes out of nowhere and is totally unconvincing. It's out of character and is just a way of setting up a forced and arbitrary conflict for the season finale.
I mean, the very least they could've done was have her say at some point that she wanted the job because it would give her more authority and access which she could use to work against the senator who had her mother killed. That would actually make some sense and fit her character. But they just ignored that angle, even though it would've clearly made the plot development far more justified. And that's damn sloppy writing.
Anyway, it's just as well that guy's political career was ended. He was far too bad a liar to get anywhere in politics.